the cr renazzo type carbonaceous chondrite group and its implications abstract a petrologic geochemical and oxygen isotopic study of eight meteorites identified as cr renazzo type chondrites reveals that they have a set of similar properties that distinguishes them from other chondrite groups and confirms cr as a carbonaceous chondrite group characteristics of the cr group include 1 1 abundant large multilayered fe ni metal rich type i chondrules 2 2 abundant matrix and dark inclusions di that contain microchondrules microfragments and magnetite framboids and platelets 3 3 unique assemblages of serpentine and chlorite rich phyllosilicates and ca carbonates 4 4 ca carbonate rims on chondrules 5 5 abundant fe ni metal with a positive ni vs co trend and a solar ni co ratio 6 6 low abundance of refractory rich inclusions 7 7 amoeboid olivine aggregates aoa with mn rich and mn poor forsterite and 8 8 oxygen isotopic compositions that form a unique mixing line the cr chondrites are breccias consisting of two major components the large layered chondrules and the matrix dark inclusions al rais is an anomalous member in having a higher abundance of the dark inclusion component 70 vol and this accounts for its having a higher volatile content than other members of the group the conditions that prevailed during aqueous alteration of the cr chondrites differed from those of other hydrated chondrite groups and may be the result of a higher temperature environment than that for the ci and cm chondrites the cr chondrite components chondrules matrix dark inclusions etc experienced aqueous alteration to differing degrees prior to assembly of the host chondrites and dark inclusions represent a lithology that was altered by water to a greater degree than the rest of the meteorite the overall degree of hydration in cr chondrites varies among meteorites with al rais being the most hydrated the oxygen isotopic variation of the whole rocks chondrules and matrices may be related to degree of hydration indicating that cr chondrites interacted with a water rich component having heavy oxygen and that was the same as ci and cm water

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

gravity anomalies and dynamics of the swiss alps an interpretation of the gravity observations in switzerland is presented the gravity anomalies are mainly caused by crustal effects taking 0 5 g cm3 as the average density contrast between crust and upper mantle the remaining positive residual field of 50 mgal can be explained as the effect of the so called lithospheric root underneath the swiss alps this root must be considered as a relatively cold body with increased density in order to calculate the thermally induced density distribution in the upper mantle a kinematic and geothermal model has been constructed simulating the alpine history for a time span covering the last 40 m y at the same time the moving lithospheric body crustal uplift and subsidence of the lower lithosphere is analysed from a dynamical point of view in order to test the kinematic conditions the calculation leads to a mantle subsidence rate of 1 mm y for the present period

recent crustal movements in switzerland and their geophysical interpretation abstract in this paper a review is presented on the most recent results of geodetically determined recent crustal movements in switzerland these data are compared with the new bouguer gravity map of switzerland and an attempt is made to discuss the geodetic and gravity results in connection with the crustal structure of the swiss alps in terms of seismic compressional wave velocities and depths to the crust mantle boundary

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

tectonics and topography for a lithosphere containing density heterogeneities the purpose of this paper is to clarify the dynamic role of lithospheric density heterogeneities in particular with respect to mountain building and other processes of intraplate deformation density anomalies within or just beneath the lithosphere constitute major sources for tectonic stress fields the product of their magnitude by their depth is shown to characterize their ability to induce deformation this rule of the density moment directly yields the lithospheric thickening or thinning rate when applied to structures of large lateral extent for anomalies of lateral extent that is small in comparison with their depth the deformation is vertically inhomogeneous and has been computed with the help of simple physical models of a stratified viscous newtonian lithosphere the analytical treatment is based on fourier transform continent continent collision thickens not only the crust but the entire lithosphere the cold root underlying a mountain chain induces strong regional compressive stresses able to sustain the mountain bulding process without further help from forces transmitted from far away thus the continental lithosphere is in a somewhat metastable mechanical state adiabatic i e rapid thickening or thinning tends to grow further once initiated tectonic phases of strong compression correspond to the climax of such instabilities the response of models with cold lithospheric roots of various intensities has been computed both in two and three dimensions they yield velocity distributions and stress fields instructive comparisons are made with earthquake focal mechanisms and in situ stress measurements in the alpine and appalachian regions in the presence of lateral variations of the mechanical properties of the lithosphere the tectonic style is not only function of the local topography and of the nature of its compensation deformations in neighbouring provinces are coupled as shown by 3 dimensional models for example thickening sustained by a cold lithospheric root may generate extension in peripheral zones of weakness these last results illustrate the point that the computation of regional tectonic stresses requires the knowledge of the density anomalies within the lithosphere on the one hand and of geometrical constraints related to lateral mechanical heterogeneities on the other

delineation of the north central italian upper mantle anomaly the italian peninsula is the focus of intense deformational tectonic activity it is underlain by mantle material whose inferred relatively anomalous properties1 2 are not inconsistent with the seismic volcanic and thermal activity that is manifested in this region the most effective geophysical tool for mapping the structure of the uppermost 200 300 km of the earth is the observation and analysis of seismic surface wave dispersion on a regional scale here we synthesize the interpretations of rayleigh wave dispersion measurements made by several authors each for different parts of north central italy3 8 to delineate the lateral extent of the upper mantle anomaly in this region

variation of mineralogy and organic material during the early stages of aqueous activity recorded in antarctic micrometeorites abstract micrometeorites mms recovered from surface snow near the dome fuji station antarctica are almost free from terrestrial weathering and contain very primitive materials and are suitable for investigation of the evolution and interaction of inorganic and organic materials in the early solar system we carried out a comprehensive study on seven porous and fluffy mms four chondritic porous cp mms and three fluffy fine grained fluffy fg mms and one fine grained type 1 fg c1 mm for comparison with scanning electron microscope transmission electron microscope x ray absorption near edge structure analysis and secondary ion mass spectrometer they show a variety of early aqueous activities four out of the seven cp mms contain glass with embedded metal and sulfide gems and enstatite whiskers platelets and do not have hydrated minerals despite the same mineralogy organic chemistry of the cp mms shows diversity two of them contain considerable amounts of organic materials with high carboxyl functionality and one of them contains nitrile c n and or nitrogen heterocyclic groups with d and 15 n enrichments suggesting formation in the molecular cloud or a very low temperature region of the outer solar system another two cp mms are poorer in organic materials than the above mentioned mms organic material in one of them is richer in aromatic c than the cp mms mentioned above being indistinguishable from those of hydrated carbonaceous chondrites in addition bulk chemical compositions of gems in the latter organic poor cp mms are more homogeneous and have higher fe si mg fe ratios than those of gems in the former organic rich cp mms functional group of the organic materials and amorphous silicate in gems in the organic poor cp mms may have transformed in the earliest stage of aqueous alteration which did not form hydrated minerals three fluffy fg mms contain abundant phyllosilicates showing a clear evidence of aqueous alteration phyllosilicates in thee mms are richer in fe than those in hydrated idps typical fine grained hydrated fg c1 mms and hydrated carbonaceous chondrites one of the fluffy fg mms contains amorphous silicate which is richer in fe than gems and contains little or no nanophase fe metal but contains fe sulfide because the chemical compositions of the amorphous silicate are within the compositional field of gems in cp idps the amorphous silicate may be alteration products of gems the entire compositional field of gems in the cp mms and the amorphous silicate in the fluffy fg mm matches that of the previously reported total compositional range of gems in idps one fluffy fg mm contains mg rich phyllosilicate along with fe rich phyllosilicate and mg fe carbonate mg rich phyllosilicate and mg fe carbonate may have been formed through the reaction of fe rich phyllosilicate mg rich olivine and pyroxene and water with c bearing chemical species these data indicate that cp mms and fluffy fg mms recovered from antarctic surface snow contain materials that throw a light on the earliest stages of aqueous alteration on very primitive solar system bodies because mineralogy and isotopic and structural features of organic materials in d10ib009 are comparable with isotopically primitive idps its parent body could be comets or icy asteroids showing mass ejection active asteroids by contrast organic poor cp mms may have experienced the earliest stage of aqueous alteration and fluffy fg mms experienced weak aqueous alteration the precursor materials of the parent bodies of fluffy fg mms probably contained abundant gems or gems like materials like cp idps which is common to fine grained matrices of very primitive carbonaceous chondrites such as cr3s however highly porous nature of organic poor cp mms and fluffy fg mms suggests that parent bodies of these mms must have been much more porous than the parent bodies of primitive carbonaceous chondrites given no phyllosilicate among the returned samples of 81p wild 2 comet the mms may have been derived from porous icy asteroids such as active asteroids as well as p and d type asteroids rather than comets

mineralogy of tagish lake an ungrouped type 2 carbonaceous chondrite in this paper we describe the recovery handling and preliminary mineralogical investigation of the tagish lake meteorite tagish lake is a type 2 carbonaceous chondrite which bears similarities to ci1 and cm chondrite groups but is distinct from both abundant phyllosilicates as well as chondrules however sparse and common olivine grains in the matrix preclude any other classification the bulk density of tagish lake 1 67 g cc which is far lower than ci or cm chondrites 2 2 2 3 and 2 6 2 9 g cc respectively or any other meteorite for that matter we have identified two lithologies a dominant carbonate poor lithology and a less abundant carbonate rich lithology the meteorite is a breccia at all scales we have noted similarities between tagish lake and some clasts within the enigmatic meteorite kaidun possibly there are genetic relationships here worth exploring in the paper we describe a clast of cm1 material within tagish lake which is very similar to a major lithology in kaidun

iron rich aureoles in the cm carbonaceous chondrites murray murchison and allan hills 81002 evidence for in situ aqueous alteration iron rich aureoles in cm carbonaceous chondrites are previously unidentified domains of aqueously altered matrix material whose feo content may exceed that of the surrounding matrix by up to more than 15 wt we describe the petrography and mineralogy of these objects in the cm chondrites murray murchison and allan hills alh 81002 the size of fe rich aureoles ranges from a few hundred microns to several millimeters in diameter and appears to be a function of the degree of alteration of the host chondrite the origin of fe rich aureoles is related to the alteration of large metal grains that has resulted in the formation of characteristic pcp rich reaction products that are frequently observed at the centers of the aureoles this suggests that fe rich aureoles in cm chondrites are the result of the mobilization of fe from altering metal grains into the matrix the fact that fe rich aureoles enclose numerous chondritic components such as chondrules calcium aluminum rich inclusions cais and mineral fragments as well as their radial symmetric appearance are strong evidence that they formed in situ and that significant directional fluid flow was not involved in the alteration process this and additional constraints such as the distribution of s and other elements as well as the inferred alteration conditions are consistent with in situ parent body alteration the observations are however entirely incompatible with preaccretionary alteration models in which the individual cm chondrite components have experienced diverse alteration histories the presence of numerous intact aureoles in the brecciated cm chondrites murray and murchison further suggests that the alteration occurred largely after brecciation affected these meteorites therefore the progressive aqueous alteration of cm chondrites may not be necessarily coupled to brecciation as has been previously proposed

ferrian saponite from the santa monica mountains california u s a earth characterization as an analog for clay minerals on mars with application to yellowknife bay in gale crater ferrian saponite from the eastern santa monica mountain near griffith park los angeles california was investigated as a mineralogical analog to smectites discovered on mars by the chemin x ray diffraction instrument onboard the mars science laboratory msl rover the martian clay minerals occur in sediment of basaltic composition and have 02 l diffraction bands peaking at 4 59 a consistent with tri octahedral smectites the griffith saponite occurs in basalts as pseudomorphs after olivine and mesostasis glass and as fillings of vesicles and cracks and has 02 l diffraction bands at that same position we obtained chemical compositions by electron microprobe x ray diffraction patterns with a lab version of the chemin instrument mossbauer spectra and visible and near ir reflectance vnir spectra on several samples from that locality the griffith saponite is magnesian mg mg fe 65 70 lacks tetrahedral fe 3 and octahedral al 3 and has fe 3 fe from 64 to 93 its chemical composition is consistent with a fully tri octahedral smectite but the abundance of fe 3 gives a nominal excess charge of 1 to 2 per formula unit the excess charge is likely compensated by substitution of o 2 for oh causing distortion of octahedral sites as inferred from mossbauer spectra we hypothesize that the griffith saponite was initially deposited with all its iron as fe 2 and was oxidized later x ray diffraction shows a sharp 001 peak at 15 a 00 l peaks and a 02 l diffraction band at the same position 4 59 a and shape as those of the martian samples indicating that the martian saponite is not fully oxidized vnir spectra of the griffith saponite show distinct absorptions at 1 40 1 90 2 30 2 32 and 2 40 m arising from h 2 o and hydroxyl groups in various settings the position of the 2 31 m spectral feature varies systematically with the redox state of the octahedrally coordinated fe this correlation may permit surface oxidation state to be inferred in some cases from vnir spectra of mars obtained from orbit and in any case ferrian saponite is a viable assignment for spectral detections in the range 2 30 2 32 m

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

paired renazzo type cr carbonaceous chondrites from the sahara ten chondrites with chemical and mineralogical similarities to the carbonaceous chondrite renazzo were recovered at two locations of the sahara acfer 059 087 097 114 139 186 187 209 270 and el djouf 001 although the el djouf location is more than 500 km away from the acfer location all samples appear to result from a single fall based on chemical and petrographic similarities and supported by light element stable isotope geochemistry noble gas record and similar 26al contents the acfer el djouf meteorite is classified as a cr renazzo type carbonaceous chondrite this group presently comprises three non antarctic members al rais renazzo acfer el djouf and five antarctic meteorites the major lithological components of the acfer el djouf meteorite are large chondrules up to 1 cm in size mean diameter 1 0 0 6 mm chondrule and mineral fragments ca al rich inclusions feni metal about 8 10 vol and dark inclusions embedded in a fine grained fragment bearing groundmass mineral compositions of the ten acfer el djouf samples are similar to those of other cr chondrites most of the ca al rich inclusions are below 300 m in size and rich in melilite and spinel in some cais the rare phase caal4o7 is dominant fo rich cr bearing olivine fa0 4 and enstatite fs0 4 are the major phases of the chondrite the meteorite is mildly shocked with a shock stage of s2 indicating a peak shock pressure of 5 10 gpa for the bulk meteorite the oxygen isotopic compositions and carbon and nitrogen stable isotope geochemistry of the acfer el djouf samples are very similar to those of the other cr type chondrites the major element composition of the acfer el djouf meteorite is indistinguishable from cr chondrites when compared to renazzo the acfer el djouf samples however have systematically lower contents of the moderately volatile elements zn ga as au sb and se and the highly volatile elements br c and n this is thought to reflect primary differences between renazzo and the acfer el djouf meteorite

petrology and geochemistry of antarctic micrometeorites abstract the petrology and geochemistry of twentythree chondritic dust particles with masses of 1 47 g sizes 100 400 m were recovered from blue ice near cap prudhomme antarctica and studied by inaa asem empa and optical microscopy sample selection criteria were irregular shape and for a subsample black color with the aim of studying as many unmelted micrometeorites mms as possible of thirteen unmelted mms six were phyllosilicate dominated mms and seven were coarsegrained crystalline mms consisting mainly of olivine and pyroxene the remaining ten particles were largely melted and consisted of a foamy melt with variable amounts of relic phases scoriaceous mms thus of the black particles selected an astonishing portion 40 by number consisted of largely unmelted mms although unmelted most phyllosilicate mms have been thermally metamorphosed to a degree that most of the phyllosilicates were destroyed but not melted the original preterrestrial mineralogy is occasionally preserved and consists of serpentine like phyllosilicates with variable amounts of cronstedtite tochilinite like oxides olivine and pyroxene the crystalline mms consist of olivine low ca pyroxene tochilinite like oxides and occasional ni poor metal relics in scoriaceous mms consist of the same phases mineral compositions and the coexistence of phyllosilicates with anhydrous phases are typical of cm and cr type carbonaceous chondrites however the olivine pyroxene ratio 1 and the lack of carbonates sulfates and of very fe poor refractory element rich olivines and pyroxenes sets the mms apart from cm and cr chondrites the bulk chemistry of the phyllosilicate mms is similar to that of cm chondrites however several elements are either depleted ca ni s less commonly na mg and mn or enriched k fe as br rb sb and au in mms as compared to cm chondrites similar depletions and enrichments are also found in the scoriaceous mms we suggest that the depletions are probably due to terrestrial leaching of sulfates and carbonates from unmelted mms the overabundance of some elements may also be due to processes acting during atmospheric passage such as the recondensation of meteoric vapors in the high atmosphere most mms are coated by magnetite of platy or octahedral habit which is rich in mg al si mn and ni we interpret the magnetites to be products of recondensation processes in the high 90 km atmosphere which are therefore probably the first refractory aerominerals identified

the textures and compositions of fine grained antarctic micrometeorites implications for comparisons with meteorites abstract micrometeorites recovered from the earth s surface constitute the most abundant interplanetary dust now falling to earth we studied eighty nine fine grained antarctic micrometeorites fg amms to evaluate their state of alteration and to identify the nature of their precursor materials fine grained amms are divided into melted and unmelted groups and subdivided on the basis of textures related to atmospheric entry heating the textures of melted particles reflect crystallisation after entry heating and those of unmelted amms broadly resemble cl cm and cr chondrite matrix the matrix compositions of the fg amms closely resemble those of cm2 chondrites matrices provide a more reliable comparison to meteorites than bulk compositions because components such as chondrules and cais are not present in representative proportions within individual amms divergences from cm like matrix compositions are generally minor and probably arose during entry heating by the dissociation of volatile bearing phases at subsolidus temperatures and evaporation and loss of immiscible metallic liquids at higher temperatures depletions in ni and mg relative to cm matrix are tentatively attributed to terrestrial weathering no conclusive evidence for contamination during atmospheric residence was observed contrary to theory textural evidence suggests that bow shocks and high thermal gradients existed during deceleration of micrometeoroids in the atmosphere

mineralogy and noble gas signatures of the carbonate rich lithology of the tagish lake carbonaceous chondrite evidence for an accretionary breccia abstract the carbonate rich lithology of the tagish lake carbonaceous chondrite was characterized by noble gas mass spectrometry synchrotron x ray diffraction analysis and transmission and scanning electron microscopy noble gas analysis was performed on two samples and the results showed that primordial noble gases are abundant and solar noble gases are absent in the samples of carbonate rich lithology the concentrations of ne a2 and e in both samples are at the maximum level observed for ci and cm chondrites suggesting high abundances of presolar diamonds and sic graphite respectively the cosmic ray exposure age cannot be determined precisely because the shielding depth of our tagish lake samples is unknown but the minimum exposure age was determined to be 5 5 0 7 myr on the basis of cosmogenic 21ne concentrations and the highest 21ne production rate x ray and electron microscopic study showed that the carbonate rich lithology is dominated by loosely packed porous matrix that consists mainly of fine grained saponite and ferromagenesian carbonate the matrix contains very few chondrules but many fine grained clasts having angular shape with longest dimensions up to 1 mm the clasts differ from host matrix in both texture and mineralogy they are massive compacted material with porosity much lower than matrix and contain abundant magnetite and a coherent intergrowth of serpentine and saponite that is rare in matrix the presence of texturally and mineralogically distinct clasts indicates that the carbonate rich lithology is a breccia but the absence of solar noble gases and impact induced deformational features in host matrix distinguish it from an asteroid regolith breccia our results instead indicate that it is an accretionary breccia formed by simultaneous accretion of diverse objects in a massive dust cloud the clasts often enclose chondrules and anhydrous silicate fragments such as low iron manganese enriched olivines this observation and their highly compacted angular morphology suggests that the clasts derive from earlier formed chondritic materials which have experienced compression and fragmentation due to mild impacts and from which they were excavated and incorporated into the final rock it is thus suggested that in the course of planetesimal formation agglomeration and disagglomeration of small parent bodies occurred repeatedly in a dense dust cloud where solar wind from the infant sun was shielded the fine grained ferromagnesian carbonates must have precipitated from aqueous solutions after the assembly of the tagish lake asteroid from recycled materials from previous bodies because the carbonates coat the surfaces of pores and fill in veins in the clasts

mineralogy and composition of matrix and chondrule rims in carbonaceous chondrites abstract the degree of compositional variation of fine grained minerals displayed by the members within any carbonaceous chondrite group i e ci cm cv cr is a direct reflection of the range of aqueous alteration assemblages present matrix and fine grained chondrule rims within any particular carbonaceous chondrite are mineralogically nearly identical to one another but not necessarily similar in bulk elemental composition even though they have subsequently experienced post accretional secondary processing aqueous alteration under identical conditions this may indicate preferential alteration of one component brecciation exchange of components between rims and matrix and or accretion of matrix and rims from mineralogically or compositionally distinct materials we propose that co chondrites experienced parent body conditions of low f o2 low water rock ratios and temperatures below 50 c cr chondrites experienced higher water rock ratios potentially higher temperatures 150 c and a wide range of f o2 the alteration mineralogy of cv chondrites indicates water rock ratios at the high end at least of the range for cr chondrites essebi and mac 87300 cm chondrites experienced temperatures below 50 c low f o2 and low water rock ratios except eet 83334 which probably experienced relatively higher f o2 and b 7904 and y 86720 which experienced postalteration temperatures in the range 500 700 c most ci chondrites experienced temperatures between 50 and 150 c relatively high water rock ratios and variable f o2 with a late stage increase in the latter due possibly to brecciation and consequent release of methane y 82162 witnessed post alteration heating possibly as high as 400 c

the cr chondrite clan implications for early solar system processes in this paper we review the mineralogy and chemistry of calcium aluminum rich inclusions cais chondrules feni metal and fine grained materials of the cr chondrite clan including cr ch and the metal rich cb chondrites queen alexandra range 94411 hammadah al hamra 237 bencubbin gujba and weatherford the members of the cr chondrite clan are among the most pristine early solar system materials which largely escaped thermal processing in an asteroidal setting bencubbin weatherford and gujba may be exceptions and provide important constraints on the solar nebula models these constraints include 1 multiplicity of cai formation 2 formation of cals and chondrules in spatially separated nebular regions 3 formation of cais in gaseous reservoir s having o 16 rich isotopic compositions chondrules appear to have formed in the presence of o 16 poor nebular gas 4 isolation of cais and chondrules from nebular gas at various ambient temperatures 5 heterogeneous distribution of al 26 in the solar nebula and 6 absence of matrix material in the regions of cai and chondrule formation

layer silicates in a chondritic porous interplanetary dust particle analytical electron microscopy on individual grains from a portion of a chondritic porous interplanetary dust particle aggregate w7029c1 from the nasa johnson space center cosmic dust collection shows that layer silicates compose 50 percent of the silicate fraction examined these layer silicates can be classified into two distinct crystallochemical groups 1 fine grained polycrystalline smectite minerals and 2 well ordered single crystals of kaolinite and mg poor talc the layer silicates in this portion of sample w7029 asterisk a are dissimilar to those described in other chondritic porous aggregates the predominant layer silicate assemblage in w7029 asterisk a indicates that heating of the aggregate during atmospheric entry was brief and probably to a temperature less than 300c comparison with terrestrial phyllosilicate occurrences suggests that some layer silicates in aggregate w7029 asterisk a may have been formed by alteratiton from preexisting silicate minerals at low temperatures less than 25c after aggregate formation

carbonaceous micrometeorites from antarctica over 100 000 large interplanetary dust particles in the 50 500 micrometers size range have been recovered in clean conditions from approximately 600 tons of antarctic melt ice water as both unmelted and partially melted dehydrated micrometeorites and cosmic spherules flux measurements in both the greenland and antarctica ice sheets indicate that the micrometeorites deliver to the earth s surface approximately 2000x more extraterrestrial material than brought by meteorites mineralogical and chemical studies of antarctic micrometeorites indicate that they are only related to the relatively rare cm and cr carbonaceous chondrite groups being mostly chondritic carbonaceous objects composed of highly unequilibrated assemblages of anhydrous and hydrous minerals however there are also marked differences between these two families of solar system objects including higher c o ratios and a very marked depletion of chondrules in micrometeorite matter hence they are chondrites without chondrules thus the parent meteoroids of micrometeorites represent a dominant and new population of solar system objects probably formed in the outer solar system and delivered to the inner solar system by the most appropriate vehicles comets one of the major purposes of this paper is to discuss applications of micrometeorite studies that have been previously presented to exobiologists but deal with the synthesis of prebiotic molecules on the early earth and more recently with the early history of the solar system

bulk mineralogical changes of hydrous micrometeorites during heating in the upper atmosphere at temperatures below 1000 c small particles 200 m in diameter from the hydrous carbonaceous chondrites orgueil ci murchison cm2 and tagish lake were experimentally heated for short durations at subsolidus temperatures under controlled ambient pressures in order to examine the bulk mineralogical changes of hydrous micrometeorites during atmospheric entry the three primitive meteorites consist mainly of various phyllosilicates and carbonates that are subject to decomposition at low temperatures and thus the brief heating up to 1000 c drastically changed the mineralogy changes included shrinkage of interlayer spacing of saponite due to loss of molecular water at 400 600 c serpentine and saponite decomposition to amorphous phases at 600 and 700 c respectively decomposition of mg fe carbonate at 600 c recrystallization of secondary olivine and fe oxide or metal at 700 800 c and recrystallization of secondary low ca pyroxene at 800 c the ambient atmospheric pressures controlled species of secondary fe phase taenite at pressures lower than 10 2 torr magnesiowstite from 10 3 to 10 1 torr and magnetite from 10 2 to 1 torr the abundance of secondary low ca pyroxene increases in the order of murchison orgueil and tagish lake and the order corresponds to saponite abundance in samples prior to heating mineralogy of the three unmelted micrometeorites f96ci024 kw740052 and kw740054 were investigated in detail in order to estimate heating conditions the results showed that they might have come from different parental objects carbonaterich tagish lake type carbonate poor tagish lake or ci type and cm type respectively and experienced different peak temperatures 600 700 and 800 900 c respectively at 60 80 km altitude upon atmospheric entry

neogene to quaternary broken foreland formation and sedimentation dynamics in the andes of nw argentina 25 s 1 the northwest argentine andes constitute a premier natural laboratory to assess the complex interactions between isolated uplifts orographic precipitation gradients and related erosion and sedimentation patterns here we present new stratigraphic observations and age information from intermontane basin sediments to elucidate the neogene to quaternary shortening history and associated sediment dynamics of the broken salta foreland this part of the andean orogen which comprises an array of basement cored range uplifts is located at 25 s and lies to the east of the arid intraorogenic altiplano puna plateau in the salta foreland spatially and temporally disparate range uplift along steeply dipping inherited faults has resulted in foreland compartmentalization with steep basin to basin precipitation gradients sediment architecture and facies associations record a three phase 10 5 and 2 ma east directed yet unsystematic evolution of shortening foreland fragmentation and ensuing changes in precipitation and sediment transport the provenance signatures of these deposits reflect the trapping of sediments in the intermontane basins of the andean hinterland as well as the evolution of a severed fluvial network present day moisture supply to the hinterland is determined by range relief and basin elevation the conspiring effects of range uplift and low rainfall help the entrapment and long term storage of sediments ultimately raising basin elevation in the hinterland which may amplify aridification in the orogen interior

transmission electron microscopy of the low ca hydrated interplanetary dust particle transmission electron microscopy of a hydrated interplanetary dust particle indicates that it consists largely of a poorly crystalline phyllosilicate containing fe mg and al with an interlayer spacing of 10 to 12aand so is distinct from the major phyllosilicate in ci and cm carbonaceous chondrites the silicate is probably an fe and mg rich smectite or mica submicron spherical to euhedral pyrrhotite and pentlandite are prominent unusual low ni 3 at ni pentlandite is also common and typically occurs as rectangular platelets unlike many chondritic interplanetary dust particles olivine is rare and pyroxene was not observed other less abundant phases are magnetite chromite and an unidentified phase containing fe mg si ca and mn this particle differs from a hydrated micrometeorite described previously by brownlee 1 indicating there are mineralogically different subsets of hydrated interplanetary dust particles despite gross similarities in mineralogy between the particle and the carbonaceous chondrites they show appreciable differences in detail

aqueous alteration and brecciation in bells an unusual saponite bearing cm chondrite the petrological and mineralogical characteristics of the unusual cm2 chondrite bells have been investigated in detail by scanning electron microscopy sem electron microprobe analysis epma and transmission electron microscopy tem bells is a highly brecciated chondrite which contains few intact chondrules a very low abundance of refractory inclusions and is notable in having an unusually high abundance of magnetite which is disseminated throughout the fine grained matrix fragmental olivines and pyroxenes are common and based on compositional data appear to have been derived from chondrules as a result of extensive brecciation the fine grained mineralogy of matrix in bells differs considerably from other cm chondrites and has closer affinities to matrix in ci chondrites the dominant phases are fine grained saponite interlayered with serpentine and phases such as tochilinite and cronstedtite which are typical of cm chondrite matrices are entirely absent pentlandite pyrrhotite magnetite anhydrite calcite and rare ti oxides also occur as accessory phases based on its oxygen and noble gas isotopic compositions zadnik 1985 rowe et al 1994 bells can be considered to be a cm2 chondrite although its bulk composition shows some departures from the typical range exhibited by this group however these variations in bulk chemistry are entirely consistent with the observed mineralogy of bells the unusual fine grained mineralogy of bells matrix can be reasonably attributed to the combined effects of aqueous alteration and advanced brecciation in a parent body environment extensive brecciation has assisted aqueous alteration by reducing chondrules and mineral grains into progressively smaller grains with high surface areas which are more susceptible to dissolution reactions involving aqueous fluids this has resulted in the preferential dissolution of fe rich chondrule olivines which are now completely absent in bells although present in other cm chondrites the formation of saponite in bells probably resulted from the dissolution of relatively silica rich phases such as pyroxene and olivine that were derived from chondrules the result of such dissolution reactions would be to increase the activity of silica in the fluid phase at least on a localized scale stabilizing saponite in preference to serpentine an increase in asio2 would also have destabilized preexisting cronstedtite which may have reacted to form magnetite and mg fe serpentine under conditions of constant o2

the volatile element enrichment of chondritic interplanetary dust particles abstract interplanetary dust particles idps collected in the stratosphere provide new information on the chemical and isotopic composition of material in the vicinity of the earth and thus possibly of asteroids and comets the available data on major minor and trace element abundances mainly obtained with pixe and syxfa suggest the presence of at least two groups of chondritic idps which differ significantly in their volatile element content the ubiquitous enrichment of volatile lithophile siderophile and chalcophile elements is most plausibly explained by atmospheric contamination and thus the question arises of the factual relationship of all properties of interplanetary dust particles to early solar system processes

a new variant of saponite rich micrometeorites recovered from recent antarctic snowfall abstract eight saponite rich micrometeorites with very similar mineralogy were found from the recent surface snow in antarctica they might have come to earth as a larger meteoroid and broke up into pieces on earth because they were recovered from the same layer and the same location of the snow synchrotron x ray diffraction xrd analysis indicates that saponite mg fe carbonate and pyrrhotite are major phases and serpentine magnetite and pentlandite are minor phases anhydrous silicates are entirely absent from all micrometeorites suggesting that their parental object has undergone heavy aqueous alteration saponite serpentine ratios are higher than in the orgueil ci chondrite and are similar to the tagish lake carbonaceous chondrite transmission electron microscope tem observation indicates that serpentine occupies core regions of fine grained saponite pyrrhotite has a low ni concentration and mg fe carbonate shows unique concentric ring structures and has a mean molar mg mg fe ratio of 0 7 comparison of the mineralogy to hydrated chondrites and interplanetary dust particles idps suggests that the micrometeorites are most similar to the carbonate poor lithology of the tagish lake carbonaceous chondrite and some hydrous idps but they show a carbonate mineralogy dissimilar to any primitive chondritic materials therefore they are a new variant of saponite rich micrometeorite extracted from a primitive hydrous asteroid and recently accreted to antarctica

extraterrestrial water in micrometeorites and cosmic spherules from antarctica an ion microprobe study the d h ratios and water contents were measured by ion microprobe analysis in 52 individual antarctic micrometeorites amms and 10 antarctic cosmic spherules acss containing nuggets of iron hydroxide cops phase in amms d values vary from 366 to 249 and water contents lie between 0 4 3 7 wt the cops nuggets in cosmic spherules have high water contents 2 to 8 wt and exhibit d values from 144 to 167 which is indicative of an extraterrestrial origin of their constituent water the silicate portion of acss also contain extraterrestrial h equivalent to 0 l to 1 2 wt water deuterium exchange experiments were performed with isotopically spiked water these experiments demonstrate that water in mineral phases of amms and acss is indigenous and does not result from contamination during residence in antarctic ice the frequency distribution of d h ratios in amms allows us to further narrow the relationship between amms and carbonaceous chondrites to cm and ci chondrites but contrasts with that of stratospheric interplanetary dust particles idps of similar sizes from 10 to 50 m the relatively narrow range of d h ratios measured in amms as well as in acss which are more resistant and thus less susceptible to collection biases suggests that d rich idp like particles are very rare in our amms collections this indicates that these d rich grains might constitute a minor fraction of the micrometeorite flux in the interplanetary medium and that possible collection biases in antarctica would not be responsible for their strong depletion in the amms collections

the microstructure of semarkona and bishunpur abstract the ordinary chondrites semarkona and bishunpur appear to have experienced in situ hydrous alteration here we report the results of the first detailed tem examination of them which supports this conclusion in semarkona all but the most magnesian mafic minerals have been destroyed and primary sulphides most likely troilite have been partially altered to phyllosilicates and ni rich pyrrhotite in bishunpur alteration is confined to the production of smectite from an amorphous feldspathic material in the chondrule rims and interchondrule matrix during hydrous alteration of both meteorites the temperature probably did not exceed 260 c the equilibrium composition of the gas present during the alteration of semarkona was not solar but was dominated by h2o the formation of smectite does not require the presence of liquid water however evidence for the redistribution of elements such as ca zn and si over tens of microns or more implies that there was at least some transient grain boundary fluid present the alteration in semarkona and bishunpur is far from complete thermodynamic modelling suggests that more altered ordinary chondrites would be mineralogically similar to the cm and ci carbonaceous chondrites superficially the mineralogy mineral chemistry and bulk chemistry of semarkona matrix rims resemble those of some chondritic interplanetary dust particles cidps the ordinary chondrite parent bodies may therefore be a source of some cidps

matrix mineralogy of the orgueil ci carbonaceous chondrite a petrographic and transmission electron microscopic study of the orgueil ci carbonaceous chondrite shows that the matrix consists mainly of fe bearing mg rich serpentine and smectite saponite as well as a poorly crystallized fe rich material that contains minor variable s and ni the fe rich material is probably ferrihydrite a ferric hydroxide the ferrihydrite occurs in small particles 80 a in diameter and the s and ni are probably adsorbed on its surfaces the serpentine and saponite occur in poorly crystallized fine crystallites fine phyllosilicates that are intimately associated with the ferrihydrite coarsely crystallized phyllosilicates coarse phyllosilicates occur in clusters relatively free of ferrihydrite the ferrihydrite is a major matrix constitutent and probably accounts for most of the fe3 as well as the superparamagnetic fraction in the orgueil matrix the textures suggest that the fine phyllosilicates resulted from alteration of the coarse phyllosilicates the alteration probably involved a substantial amount of water and coincided with the period of sulfate vein formation during the aqueous alteration magnetite grains disaggregated from framboids and fe ni sulfides were replaced by ferrihydrite simultaneously aqueous solutions reacted with the coarse phyllosilicates and precipitated ferrihydrite producing intimate pervasive mixtures with the fine phyllosilicates the matrix mineralogy of the orgueil chondrite suggests that orgueil experienced considerably different alteration conditions from the cm chondrites the mineralogical and petrological differences between ci and cm chondrites can not simply be explained as the result of different degrees of aqueous alteration

an interplanetary dust particle with links to ci chondrites abstract w7013f5 is a chondritic hydrated interplanetary dust particle whose composition and mineralogy is nearly identical to that found in the ci chondrites transmission electron microscope observations show that the phyllosilicates in w7013f5 consist largely of a coherent intergrowth of mg fe serpentine and fe bearing saponite on the unitcell scale this distinctive intergrowth of phyllosilicates has only been observed previously in the ci chondrites other secondary minerals in w7013f5 include mg fe carbonates magnetite and pentlandite the mineral assemblage in w7013f5 is generally not as oxidized as that in the ci chondrites the presence of kamacite in w7013f5 indicates that the particle is extraterrestrial and a thin amorphous rim surrounding the particle provides evidence that it is not a piece of a meteorite that fragmented during transit through the atmosphere the apparent lack of hydrated idps with ci mineralogy and chemistry may indicate that ci type dust producing asteroids are uncommon in the asteroid belt

automated thin film analyses of anhydrous interplanetary dust particles in the analytical electron microscope abstract an automated 200 kev analytical electron microscope was used to obtain elemental analyses from over 4000 points on ultramicrotomed thin sections of eight layer silicate class interplanetary dust particles idps each analysis yielded major and minor element abundances from a volume approaching that of a cylinder 50 nm in diameter multi element cluster analysis was employed to identify mineral phases and their relative abundances in the thin sections petrographic characteristics were determined using brightfield and darkfield imaging lattice fringe imaging and electron diffraction three of the particles contained smectite 1 0 1 2 nm basal spacing and two contained serpentine 0 7 nm basal spacing the mineralogy of three of the eight idps appears to have been modified by heating possibly during atmospheric entry the point count analyses and mg si fe ternary diagrams show that one of the serpentine containing idps is similar to ci and cm chondritic meteorites but the fine scale heterogeneity among the other seven is distinct from these meteorites which are more uniform on a 50 nm scale the idps exhibit evidence of aqueous processing but they have typically experienced only short range submicrometer scale alteration in comparison ci and cm chondrites are compositionally more uniform presumably as a result of more extensive aqueous alteration the hydrated layer silicate idps may provide a broad sampling of the asteroid belt including samples of the outer p and d asteroid classes

nanosized carbon rich grains in carbonaceous chondrite meteorites abstract macromolecular carbonaceous material is common in primitive meteorites little information exists on its form and composition and there are no published data on nanometer scale chemical and structural variations transmission electron microscopy tem studies of cm meteorites reveal abundant previously unrecognized nanosized carbonaceous grains they have a high aromatic component as revealed by electron energy loss spectroscopy eels with up to 20 at substituted by s n and o they occur as discrete hollow and solid nanospheres and sparse nanotubes the grains exhibit considerable variations in composition size morphology and abundance among meteorites and may represent materials from multiple reservoirs

bulk mineralogy of individual micrometeorites determined by x ray diffraction analysis and transmission electron microscopy abstract bulk mineralogy of individual fine grained micrometeorites from 50 to 200 m in diameter was determined on the basis of the powder x ray diffraction patterns and the observation of internal textures by a transmission electron microscope tem x ray diffraction analysis of 56 micrometeorites indicated that 42 11 and 3 samples are olivine rich pyroxene rich and phyllosilicate rich micrometeorites respectively among the phyllosilicate rich micrometeorites one contains saponite and other two contain serpentine no samples contain both saponite and serpentine we found that saponite rich micrometeorite was weakly heated which results in shrinkage of 001 basal spacing of saponite down to 9 7 a and that cronstedtite which is commonly contained in cm chondrites occurs in serpentine rich micrometeorites micrometeorites that consist entirely of anhydrous minerals and amorphous phases are predominant in the samples studied the major phases of such micrometeorites are olivine low ca pyroxene magnetite and fe sulfide and the average abundances are 65 17 11 and 7 wt respectively when the total abundance of the four minerals are normalized to 100 wt the relative mineral abundance varies greatly between samples low ca pyroxene olivine ratios range from 0 to 3 5 with a mean of 0 3 tem observations of inner portions of some micrometeorites revealed that they are aggregates of very small equigranular grains 100 nm of olivine magnetite or low ca pyroxene olivine magnesiowustite the textures are very similar to those of hydrous carbonaceous chondrite that was experimentally heated to temperature below melting point thus suggesting that the micrometeorites had been hydrous particles but were decomposed by the brief heating upon atmospheric entry it is newly found that magnesiowustite was formed in micrometeorites instead of magnetite as a product of phyllosilicate decomposition under low oxygen fugacity the decomposed hydrous micrometeorites gave two types of characteristic x ray diffraction patterns 1 broad olivine and magnetite reflections or 2 variable intensities of magnesiowustite reflections together with magnetite low ca pyroxene and olivine reflections twenty nine olivine or pyroxene rich micrometeorites showed such diffraction patterns thus suggesting that more than half of micrometeorites investigated must be decomposed hydrous particles the results confirmed that hydrous dust particles are much more abundant in the interplanetary space than in the micrometeorites recovered on the earth

aqueous alteration in five chondritic porous interplanetary dust particles abstract analytical electron microscope analysis of stratospheric micrometeorites show that layer silicates are common albeit minor constituents in five particles of the nominally anhydrous subclass of chondritic porous cp interplanetary dust particles idps these layer silicates are single crystal na k rich smectite minerals illite kaolinite and less common pyrophyllite mica and rare talc rare non stoichiometric crystalline feldspars of probable authigenic origin occur in cp idp w7029e5 the feldspars are low anorthite and undetermined na k alkali feldspar polymorphs similar al2o3 al2o3 sio2 ratios and alkali content of feldspars and layer silicates suggest a genetic relationship between these minerals whereby layer silicates form during aqueous alteration in the case of cp idp w7029e5 alteration occurred in a mildy acidic ph 5 7 fluid at 175 195 c if cp idps are solid debris from short period comets the observations give evidence for mineralogical and chemical activity in nuclei of short period comets if an asteroidal origin for these cp idps can be established these observations provide a window to the processes that may ultimately lead to fully hydrated carbonaceous chondrite matrices

mineralogy of phyllosilicate rich micrometeorites and comparison with tagish lake and sayama meteorites abstract four phyllosilicate rich micrometeorites mms were investigated by a synchrotron radiation x ray diffraction technique and transmission electron microscopy three are saponite rich mms and one is a serpentine rich one in the saponite rich mms we could not find serpentine and vice versa in the serpentine rich mm in the saponite rich mms major constituent minerals are saponite fe and ni bearing sulfides and magnetite two saponite rich mms contain fine grained magnesiowustite rich aggregates the aggregates consist of

mineralogy and oxygen isotope systematics of magnetite grains and a magnetite dolomite assemblage in hydrated fine grained antarctic micrometeorites

the semarkona meteorite first recorded occurrence of smectite in an ordinary chondrite and its implications abstract semarkona is an unshocked unequilibrated ordinary chondrite much of the interchondrule matrix and the mesostases of some chondrules and clasts have been hydrothermally altered analyses of altered materials and opaque matrix are presented ca and fe have been redistributed from primary anhydrous phases into calcite and na fe smectite respectively in semarkona the process possibly requires open system behavior inconsistent with the conventional view of metamorphism of the ordinary chondrites the low petrologic type previously assigned to semarkona is the result of retrograde metamorphism under aqueous conditions of a higher temperature mineral assemblage semarkona and possibly bishunpur should be assigned to petrologic type 2