indicators of aqueous alteration in cm carbonaceous chondrites microtextures of a layered mineral containing fe s o and ni a petrographic and transmission electron microscopy study of the mighei murchison and murray cm carbonaceous chondrites shows that much of the cm matrix material was probably produced by aqueous alteration of olivine pyroxene sulfide and metal the amount of cm matrix appears to be proportional to the degree of alteration as suggested by mcsween 1979 and microtextures of pcp poorly characterized phase provide evidence of the progressive alteration pcp is divided into two major types one occurs in chondrules and aggregates and consists largely of an fe ni s o phase type i and the other occurs in matrix and consists of the fe ni s o phase and cronstedtite in various proportions type ii microtextures of pcp suggest that it resulted from a three stage alteration process 1 1 type i was produced by alteration of kamacite in chondrules and aggregates presumably early in the parent body regolith 2 2 as the alteration advanced olivine and pyroxene were converted to serpentine type i pcp separated from chondrules and aggregates into the matrix during regolith gardening simultaneously the fe ni s o phase reacted with si released by alteration of olivine and pyroxene producing well formed platy cronstedtite and coherent intergrowths of the fe ni s o phase and cronstedtite the fe ni s o phase also recrystallized into platy and pod like crystals fe s ni cr and p were leached out of type i pcp and were deposited as small grains of fe ni sulfides magnetite chromite and a mineral unidentified containing fe ni cr and p as a result pcp came to consist primarily of the fe ni s o phase and cronstedtite i e type ii pcp 3 3 during continued alteration the well formed crystals of the fe ni s o phase cronstedtite and their intergrowths in type ii pcp were replaced by poorly formed fibers in comparison to other cm chondrites mighei murchison and murray are relatively unaltered their matrices retain abundant amounts of the fe ni s o phase and cronstedtite commonly as distinctive pcp grains which account for a large proportion of the fe in these meteorite matrices in more altered cm chondrites much of the fe ni s o phase was probably consumed to produce cronstedtite magnetite and sulfides with further alteration cronstedtite itself reacted with the serpentine to form ferroan serpentine thus the cm matrix was increasingly enriched in mg with alteration and pcp was increasingly degraded and intimately mixed with the magnesian phyllosilicates

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

development of a loess mudstone landslide in a fault fracture zone a landslide occurred on the morning of december 16 2013 in liujiabao village tianshui city gansu province china the 260 000 m3 of landslide material traveled a distance of 190 m downslope and damaged a village road and several farmhouses before it stopped on the middle of the slope these landslide materials are still threatening the lives and property of people in the downslope residential areas a field survey revealed that this landslide was strongly affected by the geological setting six normal faults that extend from east to west developed in the neogene mudstone of this region these faults form a fault fracture zone with a width of 80 m the authors performed a detailed investigation of the geological features of these six normal faults and their spatial and faulting relationships to the landslide were examined finally the evolutionary progress of the loess mudstone landslide controlled by the fault fracture zone is discussed

noble gas isotopes and mineral assemblages of antarctic micrometeorites collected at the meteorite ice field around the yamato mountains from november 1998 to january 1999 the 39th japanese antarctic research expedition jare conducted a large scale micrometeorite collection at 3 areas in the meteorite ice field around the yamato mountains antarctica the antarctic micrometeorites amms collected were ancient cosmic dust particles this is in contrast with the dome fuji amms which were collected previously from fresh snows in 1996 and 1997 and which represent modern micrometeorites to determine the noble gas concentrations and isotopic compositions of individual amms noble gas analyses were carried out using laser gas extraction for 35 unmelted yamato mountains amms and 3 cosmic spherules x ray diffraction analyses were performed on 13 amms before the noble gas measurement and mineral compositions were determined amms are classified into 4 main mineralogical groups defined from the heating they suffered during atmospheric entry heating temperatures of amms inferred from their mineral compositions are correlated with 4he concentrations and reflect the effect of degassing during atmospheric entry jarosite an aqueous alteration product is detected for 4 amms indicating the aqueous alteration during long time storage in antarctic ice jarosite bearing amms have relatively low concentrations of 4he which is suggestive of loss during the alteration high 3he 4he ratios are detected for amms with high 20ne 4he ratios showing both cosmogenic 3he and preferential he loss sep solar energetic particles he and ne rather than the solar wind sw were dominant in amms presumably showing a preferential removal of the more shallowly implanted sw by atmospheric entry heating the mean 20ne 22ne ratio is 11 27 0 35 which is close to the sep value of 11 2 cosmogenic 21ne is not detected in any of the particles which is probably due to the short cosmic ray exposure ages ar isotopic compositions are explained by 3 component mixing of air q and sep ar ar isotopic compositions can not be explained without significant contributions of q ar sep ne contributed more than 99 of the total ne as for 36ar and 38ar the abundance of the q component is comparable to that of the sep component 84kr and 132xe are dominated by the primordial component and solar derived xe is almost negligible

geological hazards in loess terrain with particular reference to the loess regions of china abstract the considerable morphodynamic energy provided by the continuing tectonic evolution of asia is expressed in high erosional potentials and very high rates of sediment production that make this continent unequalled as a terrestrial source of primary silt many of these environments are hazardous threatening human occupation health and livelihood especially in regions of dense population such as the loess lands of north china dry loess can sustain nearly vertical slopes being perennially under saturated however when locally saturated it disaggregates instantaneously such hydrocompaction is a key process in many slope failures made worse by an underlying mountainous terrain of low porosity rocks gully erosion of loess may yield very high sediment concentrations 60 by weight characteristic vertical jointing in loess influences the hydrology enlarged joints develop into natural sub surface piping systems which on collapse produce a loess karst terrain collapsible loess up to 20 m thick is common on the western loess plateau foundation collapse and cracked walls are common many rapid events following periods of unusually heavy monsoonal rain slope failure is a major engineering problem in thick loess terrain flow slide and spread types being common the results are often devastating in both urban and rural areas an associated hazard is the damming of streams by landslides the human population increases the landslide risk in china notably through imprudent land use practices including careless water management a number of environmentally related endemic diseases arise from the geochemistry of loess and its groundwaters including fluorosis cretinism kaschin beck disease keshan disease and goitre the chinese desert margins also have a major atmospheric dust problem the effect of such dust upon human health in these extensive regions including many large cities has yet to be evaluated but pneumoconiosis is thought to affect several million people in north and west china

analysis of chondritic interplanetary dust thin sections abstract chondritic interplanetary dust particles idps are heterogeneous aggregates of predominantly submicrometer mineral grains and carbonaceous material whose bulk compositions agree within a factor of two with type ci cm carbonaceous chondrites the mineralogy and petrography of 25 such particles were studied by analytical electron microscopic examination of ultramicrotomed thin sections 500 1000a thick four classes of chondritic idps were recognized referred to as pyroxene olivine smectite and serpentine and their relative abundances were 9 4 10 2 respectively pyroxene and olivine particles are porous assemblages of anhydrous mineral grains glass and carbonaceous material smectite and serpentine particles are low porosity objects whose matrices contain layer silicates and glassy material quantitative thin film analyses indicate that pyroxene particles most closely resemble material emitted from comet halley smectite particles may have formed from pyroxene particles by aqueous alteration of glass and enstatite crystals serpentine particles are the only class that are similar to the matrices of carbonaceous chondrites but these are the least abundant chondritic idps collectively chondritic particles are a mineralogically diverse group of extraterrestrial materials

chondrules in antarctic micrometeorites previous studies of unmelted micrometeorites 50 m recovered from antarctic ice have concluded that chondrules which are a major component of chondritic meteorites are extremely rare among micrometeorites we report the discovery of eight micrometeorites containing chondritic igneous objects which strongly suggests that at least a portion of coarse grained crystalline micrometeorites represent chondrule fragments six of the particles are identified as composite micrometeorites that contain chondritic igneous objects and fine grained matrix these particles suggest that at least some coarse grained micrometeorites cgmms may be derived from the same parent bodies as fine grained micrometeorites the new evidence indicates that contrary to previous suggestions the parent bodies of micrometeorites broadly resemble the parent asteroids of chondrulebearing carbonaceous chondrites

laihunite and jarosite in the yamato 00 nakhlites alteration products on mars 1 nakhlites martian clinopyroxenites are believed to have experienced aqueous alteration on the martian surface on the basis of the presence of reddish brown iddingsite on the rim and along cracks of large olivine crystals amorphous to poorly crystalline phyllosilicates smectites and carbonates are major products of aqueous alteration of the yamato 00 nakhlites the yamato 000593 nakhlite and its pair yamato 000749 contain large olivine crystals having opaque black material intimately associated with iddingsite on their rims and along cracks synchrotron radiation x ray diffraction micro raman spectroscopy and transmission electron microscopy revealed that the opaque material is the nonstoichiometric olivine type mineral laihunite 0 42 mg2 fe2 0 79fe3 0 79si1 00o4 typically formed as a high temperature oxidation product under nonequilibrium conditions because laihunite has been decomposed into a mixture of magnetite and amorphous silicate near the fusion crust it is preterrestrial in origin this is the first observation of large olivine crystals in martian meteorites being replaced by laihunite although its presence in olivine in the mesostasis of the miller range 03346 nakhlite has been suggested by micro raman spectroscopy because laihunite in the nakhlites does not form nanometer sized intergrowth with iron oxides fluid assisted high temperature oxidation may have played an important role in transporting away free fe2 cations liberated from olivine during laihunite formation although the yamato 00 nakhlites also contain jarosite we could not confirm the presence of preterrestrial jarosite based only on its occurrences

cm like interplanetary dust particles in lower stratosphere during 1989 october and 1991 june july the stratospheric interplanetary dust particles l2005t12 and l2011o3 are linked to cm chondrite matrix particle l2005t12 is dominated by tabular grains of partially dehydrated greenalite rich serpentine its amorphous matrix contains abundant smectite nanocrystals and annular fe ni s units a uniquely stratified partial maghemite rim occurs only on s rich parts of the matrix formation of this rim and mg depletions in the matrix occurred during atmospheric entry heating of this particle particle l2011o3 has large iron sulfide and magnesiowustite grains in an amorphous low al ferromagnesiosilica matrix hydrous crystallisation of this matrix produced ultrafine grained smectites and disseminated iron sulfides atmospheric entry heating of both particles is indicated by the partial iron oxide rim vesicular sulfides and the scatter of matrix compositions due to loss of mg while many uncertainties remain the high incidence of chondritic rough particles which include an unknown amount of cm like particles in the lower stratosphere during 1984 1989 and 1991 suggests annual variations in their abundances the timing of lower stratospheric dust samplings is critical to collect these particles

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

shock fabrics in fine grained micrometeorites the orientations of dehydration cracks and fracture networks in fine grained unmelted micrometeorites were analyzed using rose diagrams and entropy calculations as cracks exploit pre existing anisotropies analysis of their orientation provides a mechanism with which to study the subtle petrofabrics preserved within fine grained and amorphous materials both uniaxial and biaxial fabrics are discovered often with a relatively wide spread in orientations 40 60 brittle deformation cataclasis and rotated olivine grains are reported from a single micrometeorite this paper provides the first evidence for impact induced shock deformation in fine grained micrometeorites the presence of pervasive low grade shock features in cm chondrites and cm like dust anomalously low density measurements for c type asteroids and impact experiments which suggest cm chondrites are highly prone to disruption all imply that cm parent bodies are unlikely to have remained intact and instead exist as a collection of loosely aggregated rubble pile asteroids composed of primitive shocked clasts

hydrochemistry of geothermal water in tianshui and adjacent area gansu province china a geochemical study on thermal water has been carried out in tianshui and its adjacent area gansu province china chemical and isotopic contents were employed in the investigation on the origin and evolution of thermal water and the evaluation of reservoir temperature in the geothermal systems thermal waters in wushan and tianshui are characterized by outlet temperatures from 15 to 38 c and low tds 226 255 mg l defined as bicarbonate water its origin may be attributed to the interaction between meteoric rain biotite plagioclase gneiss and carbonate reservoir rocks in contrast thermal waters in tongwei and qingshui have higher outlet temperatures of 25 54 2 c and a moderate tds of 915 1 793 mg l regarded as sulfate waters these sulfate waters may arise from the interaction between meteoric water granite and amphogneiss isotopic data presented here suggest that thermal waters in the study area have a meteoric origin without being significantly effected by water rock isotope exchange chemical geothermometry indicates the existence of a deep geothermal reservoir of low to medium enthalpy 70 111 c in the tianshui study area

properties and microstructure of a natural slip zone in loose deposits of red beds southwestern china abstract the loose deposits of red beds located in southwestern china are vulnerable to the occurrence of landslides in this paper a shallow progressive landslide developed in loose deposits of red beds was selected as a case study and the physical and mechanical properties of the main slip zone were analyzed in detail it was observed that the main slip zone of the progressive landslide is composed of fine grained soils with substantial amounts of expansive clay particles interlayered illite smectite and interlayered chlorite smectite the one dimensional consolidation test of the residual soils shows that the soils are overconsolidated the shear stress versus shear displacement curves reveal that the slip zone soil has exhibited a strain softening behavior the residual friction angle of the undisturbed slip zone soil determined by the ring shear tests is 7 2 indicating that the residual strength of the soil is very low when in a saturated state the microstructure of the slip zone was investigated using a combination of images captured by means of polarising microscopy pm and scanning electron microscope sem techniques it was found that the slip zone possessed generally softer structure with higher relative porosities than its confining materials the microstructure of the slip zone is generally characterized by its softer structure and higher degree of alignment of fine silts suggesting that the slip zone underwent two deformation processes i e dilatancy and particle rearrangement the global mechanical behavior of the investigated slip zone may be conceptualized as an overconsolidated clayey soil under drained conditions

yamato 86029 aqueously altered and thermally metamorphosed ci like chondrite with unusual textures we describe the petrologic and trace element characteristics of the yamato 86029 y 86029 meteorite y 86029 is a breccia consisting of a variety of clasts and abundant secondary minerals including coarse and fine grained phyllosilicates fe ni sulfides carbonates and magnetite there are no chondrules but a few anhydrous olivine rich grains are present within a very fine grained phyllosilicate rich matrix analyses of 14 thermally mobile trace elements suggest that y 86029 experienced moderate open system thermal metamorphism comparison with data for other heated carbonaceous chondrites suggests metamorphic temperatures of 500 600 oc for y 86029 this is apparent petrographically in partial dehydration of phyllosilicates to incompletely re crystallized olivine this transformation appears to proceed through intermediate highly disordered poorly crystalline phases consisting of newly formed olivine and residual desiccated phyllosilicate and their mixtures periclase is also present as a possible heating product of mg rich carbonate precursors y 86029 shows unusual textures rarely encountered in carbonaceous chondrites the periclase occurs as unusually large fe rich clasts 300 500 m fine grained carbonates with uniform texture are also present as small 10 15 m in diameter rounded to sub rounded shells of ankerite siderite enclosing magnetite these carbonates appear to have formed by low temperature aqueous alteration at specific thermal decomposition temperatures consistent with thermodynamic models of carbonate formation the fine and uniform texture suggests crystallization from a fluid circulating in interconnected spaces throughout entire growth one isolated aggregate in y 86029 also consists of a mosaic of polycrystalline olivine aggregates and sulfide blebs typical of shock induced melt re crystallization except for these unusual textures the isotopic petrologic and chemical characteristics of y 86029 are quite similar to those of y 82162 the only other heated ci like chondrite known they were probably derived from similar asteroids rather than one asteroid and hence may not necessarily be paired

composition and accretion rate of fossil micrometeorites recovered in middle triassic deep sea deposits micrometeorites which are submillimeter sized extraterrestrial particles that survive atmospheric entry originate from dust producing objects such as comets and asteroids although ancient micrometeorites found in sedimentary rocks are of key interest as a historical record of meteoroid populations in the solar system they are rare and prone to severe chemical weathering here we report the recovery of well preserved micrometeorites older than 240 ma in radiolarian chert from japan the collection of micrometeorites comprised 258 cosmic spherules which are particles that totally melted during atmospheric entry and 2 coarse grained unmelted micrometeorites these micrometeorites are much older than any previous micrometeorite collection in the sedimentary record using this collection we calculated the accretion rate of iron type cosmic spherules to the earth during the anisian stage of the middle triassic the estimated accretion rate for anisian iron type spherules smaller than 125 m is 25 8 t yr 1 analysis of the accretion rate for cosmic spherules also reveals high accretion rates of small spherules 8 36 m for a 0 74 m y period in the late anisian however the possible link between an enhancement in the accretion rate of small cosmic spherules in the late anisian and variations in the flux of extraterrestrial matter to the earth requires further scrutiny

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 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

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

neon measurements of individual greenland sediment particles proof of an extraterrestrial origin and comparison with edx and morphological analyses abstract the work reported here confirms the existence of largely unmelted micrometeorites in sediments from seasonal lakes on the greenland ice sheet approximately1 3 of the dark and irregularly shaped particles selected from disaggregated sediments had sufficient contents of ne to permit measurement of isotopic compositions the sediments consisted of a mixture of biologically derived contaminants and minor amounts of terrestrial minerals and extraterrestrial fragments although terrestrial mineral contamination varied by a factor of 20 for the two different sediments a yield of 1000 cosmic particles kg of wet cryoconite was found for both samples the isotopic compositions of the ne in both rounded and irregular 25 of total particles that contained enough gas to measure were non terrestrial plotting in a field defined by solar wind sw solar energetic particle sep and spallation exposure ages ranged from

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

oxygen isotopic and chemical compositions of cosmic spherules collected from the antarctic ice sheet implications for their precursor materials abstract bulk chemical compositions and oxygen isotopic compositions were analyzed for 48 stony cosmic spherules melted micrometeorites collected from the antarctic ice sheet using electron and ion microprobes no clear correlation was found between their isotopic compositions and textures the oxygen isotopic compositions showed an extremely wide range from 28 to 93 in 18o and from 21 to 13 in 17o in 18o 17o space most samples 38 out of 48 plot close to the terrestrial fractionation line but 7 samples plot along the carbonaceous chondrite anhydrous mineral ccam line three samples plot well above the terrestrial fractionation line one of these has a 17o of 13 the largest value ever found in solar system materials one possible precursor for this spherule could be 16o poor planetary material that is still unknown as a meteorite the majority of the remaining spherules are thought to be related to carbonaceous chondrites

origin of the magnetic susceptibility signal in chinese loess abstract the quality of the loess magnetic susceptibility ms record as a climate proxy has been compared to the ice core and deep sea records yet the source and causes of the ms signal remain poorly understood four explanations are currently in circulation the dominant hypothesis that ms variations largely result from post depositional weathering and or formation of magnetic phases by pedogenic processes has led to the use of ms data as a palaeoprecipitation proxy we present a different view based on analyses of samples of monthly dust falls over 4 years in north china these have ms values comparable to those of pleistocene loess and palaeosols but unlike the latter their variations are seasonal and so cannot be explained by weathering differences our experiments confirm that ms enhancement in the palaeosols is caused principally by fine grain magnetic minerals but in contrast with previous proposals the major source of the ultrafine magnetic minerals appears to be decomposed plant litter

microstructural observations of shear zones in sensitive clay abstract the present work assesses the structure and evolution of shear zones in sensitive quick clays from the initiation to the well established state this assessment is done by utilizing laboratory and small scale field experiments combined with the analysis of thin sections in light microscopy and sem high resolution x ray tomography micro ct is also applied in combination detailed 2d and 3d visualization of the shear zones is achieved shear zones are suggested to be formed in mm thick continuous fields of displacement with increasing shear displacement sets of micron sized minor shears develop within the main shear zone these initiate terminate and merge both in the plane and out of the plane directions the minor shears are characterized by distinct particle reorientation where the flaky clay particles and mica grains are aligned parallel to the direction of shear a porosity reduction is observed in the minor shears this is a direct observation of material contractancy and implies migration of water from the shear zone into the undisturbed matrix the width of the main shear zone is considered to be related to the applied rate of shear while the minor shears have a width determined by the micro texture of the sediment the observed multi scale structure of the shear zones which is governed by complex inner mechanics is challenging the smooth shear zone concept that is commonly applied in numerical simulations this is motivating a further improvement of such tools and the testing of other types of clay sediments

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

heavy rainfall triggered loess mudstone landslide and subsequent debris flow in tianshui china abstract continuous and heavy precipitation triggered a large loess landslide at the southern dagou village of mapaoquan town tianshui city gansu province of china on july 21 2013 the landslide debris rapidly turned into a debris flow that was deposited in the ravine mouth with the volume of 1 9 105 m3 detailed field mapping three dimensional laser scanning aerial photograph interpretation and laboratory tests were carried out to study the formation and moving characteristics of the landslide and subsequent debris flow the results showed that 1 the peak flow velocity and peak discharge of the debris flow were estimated to be approximately 7 2 m s and 730 m3 s respectively the velocity had a tendency to first increase and then decrease from the head to entrance in the dagou gully 2 the analysis of rainfall conditions showed that the effective antecedent rainfall within 7 days and hourly rainfall intensity which triggered the slide debris flows was 239 mm and 20 mm h respectively compared with the critical rainfall in this area the effective antecedent rainfall was found to be more significant in triggering this event 3 the mean and effective particle sizes were approximately 0 73 1 3 mm and 0 036 0 087 mm respectively and had the same distribution along the gully as the velocity which confirmed the process of the variation in the flow velocity 4 the scale amplification was very obvious in the formation and moving process of the slide debris flows

an assessment of the meteoritic contribution to the martian soil the addition of meteoritic material to the mars soils should perturb their chemical compositions as has been detected for soils on the moon anders et al 1973 and sediments on earth kyte and wasson 1986 using the measured mass influx at earth and estimates of the mars earth flux ratio we estimate the continuous planet wide meteoritic mass influx on mars to be between 2700 and 59 000 t yr if distributed uniformly into a soil with a mean planetary production rate of 1 m b y consistent with radar estimates of the soil depth overlaying a bouldered terrain in the tharsis region christensen 1986 our estimated mass influx would produce a meteoritic concentration in the mars soil ranging from 2 to 29 by mass analysis of the viking x ray fluorescence data indicates that the mars soil composition is inconsistent with typical basaltic rock fragments but can be fit by a mixture of 60 basaltic rock fragments and 40 meteoritic material clark and baird 1979 the meteoritic influx we calculate is sufficient to provide most or all of the material required by the clark and baird 1979 model particles in the mass range from 10 7 to 10 3 g about 60 200 m in diameter contribute 80 of the total mass flux of meteoritic material in the 10 13 to 106 g mass range at earth hughes 1978 on earth atmospheric entry all but the smallest particles generally 50 m in diameter in the 10 7 to 10 3 g mass range are heated sufficiently to melt or vaporize mars because of its lower escape velocity and larger atmospheric scale height is a much more favorable site for unmelted survival of micrometeorites on atmospheric deceleration we calculate that a significant fraction of particles throughout the 60 1200 m diameter range will survive mars atmospheric entry unmelted thus returned mars soils may offer a resource for sampling micrometeorites in a size range which is not collectable in unaltered form at earth

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

effects of rainwater softening on red mudstone of deep seated landslide southwest china abstract red mudstone landslides are widespread in southwest of china the development and distribution of deep seated landsides with slow inclination are closely related to the special soft rock properties of the red mudstone layers most previous studies focused on the failure mechanisms of rain induced shallow landslides studies on deep seated landslides in red layer zones are still limited in order to ascertain the basic failure mechanisms of red layer landslides with a gentle inclination a fatal landslide named as shibangou landslide which occurred in sichuan china was investigated this paper aims to 1 conduct laboratory tests on the reduction in shear strength of a red layer to identify the water rock coupling effect 2 investigate variations in the microscopic structure of the soft rock found within a red layer after rainfall infiltration 3 discuss the failure mechanisms of red layer landslides with slow inclination results from shear test of mudstone from the shibangou landslide revealed that there is a tendency that behavior of soft rock can be transferred to soil in different days of immersion the delineation threshold of shear strength of the red layer is determined as 6 days of immersion microstructures of clay minerals become loose and porous due to the contacts between the particles transferred from the face edges face face associations into edge edge and face edge associations therefore the intramolecular and cemented expansions of illite are the basic mechanisms which lead to structural damage structural decay and strength attenuation of soft rock in red layer under the condition of rainwater infiltration

carbon abundance and silicate mineralogy of anhydrous interplanetary dust particles we have studied nineteen anhydrous chondritic interplanetary dust particles idps using analytical electron microscopy we have determined a method for quantitative light element edx analysis of small particles and have applied these techniques to a group of idps our results show that some idps have significantly higher bulk carbon abundances than do carbonaceous chondrites we have also identified a relationship between carbon abundance and silicate mineralogy in our set of anhydrous idps in general these particles are dominated by pyroxene olivine or a subequal mixture of olivine and pyroxene the pyroxene dominated idps have a higher carbon abundance than those dominated by olivines members of the mixed mineralogy idps can be grouped with either the pyroxene or olivine dominated particles based on their carbon abundance the high carbon pyroxene dominated particles have primitive mineralogies and bulk compositions which show strong similarities to cometary dust particles we believe that the lower carbon olivine dominated idps are probably derived from asteroids based on carbon abundances the mixed mineralogy group represents particles derived from either comets or asteroids we believe that the high carbon pyroxene rich anhydrous idps are the best candidates for cometary dust

mineralogy of carbonaceous chondritic microclasts in howardites identification of c2 fossil micrometeorites abstract seventy one carbonaceous chondritic microclasts of average size 150 m have been found in three howardites yamato 793497 jodzie kapoeta all carbonaceous chondritic microclasts are made of a fine grained phyllosilicate rich matrix supporting a variety of minerals such as olivine pyroxene spinel iron oxides iron nickel sulfides and calcium carbonates such a mineralogy is typical of chondritic c2 matter half of the carbonaceous chondritic microclasts are tochilinite rich and have been tentatively called cm2 microclasts the other half are magnetite rich and have been tentatively called cr2 microclasts the absence of a correlation between the cm2 cr2 ratio in carbonaceous chondritic microclasts and in numerous millimeter sized clasts found in the same sections argues for carbonaceous chondritic microclasts being true micrometeorites rather than fragments of larger objects dynamical simulations show that it is possible for asteroidal dust to encounter vesta the howardite s putative parent asteroid at velocity low enough 1 to prevent fragmentation because the micrometeorite flux in the inner solar system has been decreasing with time we argue that carbonaceous chondritic microclasts have been trapped in vesta s regolith early in the history of the solar system and are fossil micrometeorites because both microclasts and clasts found in howardites are related to c2 chondritic matter we propose that c2 matter represents the bulk or at least a significant fraction of the primordial howardite parent asteroid considering the abundance of c2 matter among fossil micrometeorites we speculate that the c2 fossil micrometorites are the so far unidentified agent of the late chondritic veneer that endowed the earth s mantle with an excess of siderophile elements relative to the contents predicted by the core mantle separation models the discovery that c2 fossil micrometeorites are similar to c2 modern antarctic micrometeorites supports recent models proposing a micrometeoritic origin for the earth s oceans and volatile species

small antarctic micrometeorites a mineralogical and in situ oxygen isotope study we have investigated the texture bulk chemistry mineralogy as well as the anhydrous minerals oxygen isotopic composition of 67 small antarctic micrometeorites amms collected at cap prudhomme antarctica and belonging to the currently poorly studied size fraction 25 50 m when compared to larger 50 400 m micrometeorites collected at the same site in antarctica with the same techniques no significant differences are found between the two populations we therefore conclude that the population of cap prudhomme amms is homogeneous over the size range 25 400 m in contrast small amms have different textures mineralogy and oxygen isotopic compositions than those of stratospheric interplanetary dust particles idps because small amms 50 m overlap in size with idps the differences between these two important sources of micrometeorites can no longer be attributed to a variation of the micrometeorite composition with size physical biases introduced by the collection procedures might account for these differences

assessment of the liquefaction susceptibility of fine grained soils observations from recent earthquakes and the results of cyclic tests indicate that the chinese criteria are not reliable for determining the liquefaction susceptibility of fine grained soils fine grained soils that liquefied during the 1994 northridge 1999 kocaeli and 1999 chi chi earthquakes often did not meet the clay size criterion of the chinese criteria cyclic testing of a wide range of soils found to liquefy in adapazari during the kocaeli earthquake confirmed that these fine grained soils were susceptible to liquefaction it is not the amount of clay size particles in the soil rather it is the amount and type of clay minerals in the soil that best indicate liquefaction susceptibility thus plasticity index pi is a better indicator of liquefaction susceptibility loose soils with pi 0 85 were susceptible to liquefaction and loose soils with 12 0 8 were systematically more resistant to liquefaction soils with pi 18 tested at low effective confining stresses

rotational translational landslides in the neogene basins at the northeast margin of the tibetan plateau abstract rotational translational landslides are common in neogene basins throughout the world and are of high risk to the public to understand the mechanism of rotational translational failure the spatial distribution and deformation of rotational translational landslides in the northeast of the tibetan plateau are investigated in this study the spatial distribution of these landslides is dependent on the regional tectonics and geomorphology crustal stresses and lithological properties the rotational translational landslides are concentrated in the neogene mudstone basins and the intensities of these landslides are observed to gradually decrease from the hinterland of the plateau to the marginal basins the bedding parallel shear zones within the location of the rotational translational landslides are present in the overconsolidated neogene mudstones with high clay content nearly horizontal tectonic stresses and erosion cause the formation of horizontal shear stresses in the sliding masses in this stress environment materials with low internal friction angle

heating effects of the matrix of experimentally shocked murchison cm chondrite comparison with micrometeorites micrometeorites have been significantly altered or melted by heating which has been mainly ascribed to aerodynamic drag during atmospheric entry however if a major fraction of micrometeorites are produced by impacts on porous asteroids they may have experienced shock heating before contact with the earth s atmosphere tomeoka et al 2003 a transmission electron microscope tem study of the matrix of murchison cm chondrite experimentally shocked at pressures of 10 49 gpa shows that its mineralogy and texture change dramatically mainly due to shock heating with the progressive shock pressures tochilinite is completely decomposed to an amorphous material at 10 gpa fe mg serpentine is partially decomposed and decreases in amount with increasing pressure from 10 to 30 gpa and is completely decomposed at 36 gpa at 49 gpa the matrix is extensively melted and consists mostly of aggregates of equigranular grains of fe rich olivine and less abundant low ca pyroxene embedded in si rich glass the mineralogy and texture of the shocked samples are similar to those of some types of micrometeorites in particular the samples shocked at 10 and 21 gpa are similar to the phyllosilicate serpentine rich micrometeorites and the sample shocked at 49 gpa is similar to the olivine rich micrometeorites the shock heating effects also resemble the effects of pulse heating experiments on the ci and cm chondrite matrices that were conducted to simulate atmospheric entry heating we suggest that micrometeorites derived from porous asteroids are likely to go through both shock and atmospheric entry heating processes

microstructural study of a natural slip zone quantification and deformation history abstract microstructure of a natural slip zone was comprehensively examined using a combination of images captured systematically by optical microscopy opm and backscattered electron microscopy bem techniques microstructural features identified on these images were processed and evaluated using an advanced image analysis system which proved that quantitative analyses could considerably enhance the understanding of shear behavior of slip zones it was found that variations of porosity abundance of platy clay particles and alignments of particles are significant indicators revealing nature of deformation processes these indicators show that global mechanical behavior of the investigated slip zone can be conceptualized as that of normally consolidated clayey soils under drained conditions the geometric patterns of the microstructure of the slip zone are similar to the s c fabrics seen in tectonic shear zones it is suggested that combined progressive bulk simple shear and pure shear modes enable to realistically reconstruct the kinematic history of the slip zone through which particle movements and microstructural evolution were accomplished via various types of particulate flows the results of this study show that clay mineralogy plays a more important role in the development of the slip zone than abundance of clay size particles while both clay mineralogy and relative proportions of each particle size fraction control the response of particles to shear deformation among the fractions present in the slip zone fine silts are the strongest indicator of global shear stress characterized by their highest degree of alignment whereas clay particles are the weakest highest degree of shape preferred orientation is also found within fine silt domains

petrographic chemical and spectroscopic evidence for thermal metamorphism in carbonaceous chondrites i ci and cm chondrites abstract we present a comprehensive description of petrologic chemical and spectroscopic features of thermally metamorphosed ci like and cm and cm like chondrites only two such ci chondrites have so far been discovered i e y 86029 and y 82162 thermal metamorphism in these chondrites is apparent in their low contents of h2o c and the most thermally labile trace elements partial dehydration of matrix phyllosilicates and abundance of thermally decomposed ca mg fe mn carbonates which apparently resulted from heating of mg fe carbonate precursors the cm chondrites exhibit a wide range of aqueous and thermal alteration characteristics this alteration was almost complete in y 86720 and y 86789 which also escaped alternating episodes of oxidation and sulfidization experienced by the others thermal metamorphism in the cm chondrites is apparent in loss of thermally labile trace elements and also in partial to almost complete dehydration of matrix phyllosilicates heating was less uniform in them than in ci chondrites this dehydration is also evident in strength and shapes of integrated intensities of the 3 m bands except in pca 91008 which experienced extensive terrestrial weathering tochilinite is absent in all but y 793321 probably due to heating textural evidence for thermal metamorphism is conspicuous in blurring or integration fusion of chondrules with matrix in the more extensively heated 600 c cm chondrites like pca 91008 and b 7904 tem and xrd analyses reveal that phyllosilicate transformation to anhydrous phases proceeds via poorly crystalline highly desiccated and disordered intermediate phases in the least and moderately heated 400 600 c carbonaceous chondrites like wis 91600 pca 91008 and y 86029 these findings are significant in that they confirm that these phases occur in meteorites as well as terrestrial samples thermal alteration in these meteorites can be used to identify other carbonaceous chondrites that were thermally metamorphosed in their parent bodies combining rnaa trace element data for experimentally heated murchison cm2 samples with petrographic and spectroscopic data these thermally metamorphosed carbonaceous chondrites can be ordered by severity of open system heating as 400 c y 793321

iron and iron nickel sulfides in chondritic interplanetary dust particles abstract we report the results of a study of iron and iron nickel sulfides in chondritic anhydrous and hydrated interplanetary dust particles idps the idps were characterized using chemical and mineralogical techniques including energy dispersive x ray analyses and transmission electron microscopy it is widely believed that the first sulfur containing mineral to form in the early solar nebula should have been stoichiometric fes troilite and that pyrrhotite is of secondary origin all examined interplanetary dust particles both anhydrous and hydrous types contain more pyrrhotite than troilite suggesting that the former was a common possibly predominant nebular condensate phase pyrrhotite could form from sulfidation of troilite after the latter had exfoliated from substrate metal grains in contrast to anhydrous idps hydrated ones contain ni rich sulfides including pentlandite which are probably of secondary origin

the role of seismic triggering in a deep seated mudstone landslide china historical reconstruction and mechanism analysis abstract deep seated mudstone landslides are widely distributed in northwest china the zhengjiamo landslide occurred in 734 ce near taijing tianshui region it was triggered by the main shock of the historical ms 7 0734 ce earthquake the earthquake also induced a wide range of landslides in this area with hundreds of fatalities and many houses destroyed by landslide debris based on a detailed field survey borehole data and mapping a detailed geological reconstruction of the slope was achieved and the geo mechanical features of the claystone involved in the landslide were obtained using the particle flow code to simulate the mechanism of the zhengjiamo landslide the features of the landslide dynamics were obtained using a 5 stage model during the landslide process the slip mass at the front and upper edges exhibited higher mobility than at the rear and bottom edges furthermore the contact bond strength of the sliding body gradually weakened the model indicates that the particle bond strength has a larger influence on the maximum runout distance and landslide debris morphology than the type of weak intercalated layers the slip mass presented a rotational slide pattern and remained on the slip plane throughout the sliding process finally the earthquake uplifted the slope toe which prevented the slip mass from gliding the modelled scenario provided a reasonably good fit to the actual topography verifying the modelling results after the historical earthquake with the clay minerals swelling and shrinking under rainfall and efflorescence conditions the structure of the soft rock changed contributing to the weakening of the sliding rock mass the landslide gradually crept and evolved to its current topography

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

sodic plagioclase thermometry of type 6 ordinary chondrites implications for the thermal histories of parent bodies the structural states of sodic plagioclase crystals of 50 m in size from three h6 two l6 and one ll6 chondritic meteorites have been determined by measuring the 131 parameter with a gandolfi camera after analyzing chemical compositions the temperature for each sodic plagioclase crystal has been determined by plotting the 131 parameter corrected for the influence of k on the relation diagram between the 131 parameter and the temperature of synthesis of sodic plagioclase by smith 1972 the temperature obtained is assigned to the crystallization temperature of sodic plagioclase and the maximum plagioclase temperature for each meteorite can be assumed to correspond to the maximum temperature attained by each meteorite during metamorphism the maximum metamorphic temperatures estimated are 725 742 c for the h6 chondrites 808 820 c for the l6 chondrites and 800 c for the ll6 chondrite these temperatures are lower than those based on ca contents of clinopyroxenes dodd 1981 mcsween et al 1988 but are consistent with those based on ca contents of orthopyroxenes mcsween and patchen 1989 langenhorst et al 1995 jones 1997 the k content of sodic plagioclase correlates with the temperature obtained from the structural state this positive correlation suggests that sodic plagioclase has formed in the course of equilibration processes of alkali elements in prograde metamorphism i e during heating processes the results of this study i e the maximum metamorphic temperature of the h6 chondrites is lower than that of the l6 chondrites by 80 c and meteorites of the same chemical group show very similar maximum metamorphic temperatures are in accordance with the predictions of calculations based on the 26al heat source and the onion shell structure model of the parent bodies

stardust in antarctic micrometeorites we report the discovery of presolar silicate oxide hibonite and possibly sic grains in four antarctic micrometeorites amms the oxygen isotopic compositions of the eighteen presolar silicate and one oxide grains found are similar those observed previously in primitive meteorites and interplanetary dust particles and indicate origins in oxygen rich red giant or asymptotic giant branch stars or in supernovae four grains with anomalous c isotopic compositions were also detected 12c 13c as well as si ratios are similar to those of mainstream sic grains the n isotopic composition of one grain is also consistent with a mainstream sic classification presolar silicate grains were found in three of the seven amms studied and are heterogeneously distributed within these micrometeorites fourteen of the 18 presolar silicate grains and 3 of the 4 c anomalous grains were found within one amm t98g8 presolar silicate bearing micrometeorites contain crystalline silicates that give sharp x ray diffractions and do not contain magnesiowstite which forms mainly through the decomposition of phyllosilicates and carbonates the occurrence of this mineral in amms without presolar silicates suggests that secondary parent body processes probably determine the presence or absence of presolar silicates in antarctic micrometeorites

heating experiments simulating atmospheric entry heating of micrometeorites clues to their parent body sources depending on their velocity entry angle and mass extraterrestrial dust particles suffer certain degrees of heating during entry into earth s atmosphere and the mineralogy and chemical composition of these dust particles are significantly changed in the present study pulse heating experiments simulating the atmospheric entry heating of micrometeoroids were carried out in order to understand the mineralogical and chemical changes quantitatively as well as to estimate the peak temperature experienced by the particles during entry heating fragments of the ci chondrites orgueil and alais as well as pyrrhotites from orgueil were used as analogue material the experiments show that the volatile elements s zn ga ge and se can be lost from 50 to 100 m sized ci meteorite fragments at temperatures and heating times applicable to the entry heating of similar sized cosmic dust particles it is concluded that depletions of these elements relative to ci as observed in micrometeorites are mainly caused by atmospheric entry heating besides explaining the element abundances in micrometeorites the experimentally obtained release patterns can also be used as indicators to estimate the peak heating of dust particles during entry using the abundances of zn and ge and assuming their original concentrations close to ci a maximum heating of 1100 1200 c is obtained for previously analyzed antarctic micrometeroites thermal alteration also strongly influenced the mineralogy of the meteorite fragments while the unheated samples mainly consisted of phyllosilicates these phases almost completely transformed into olivine and pyroxene in the fragments heated to 800 c therefore dust particles that still contain hydrous minerals were probably never heated to temperatures 800 c in the atmosphere during continued heating the grain size of the newly formed silicates increased and the composition of the olivines equilibrated applying these results quantitatively to antarctic micrometeorites typical peak temperatures in the range of 1100 1200 c during atmospheric entry heating are deduced this temperature range corresponds to the one obtained from the volatile element concentrations measured in these micrometeorites and points to an asteroidal origin of the particles

yamato 793321 cm chondrite dehydrated regolith material of a hydrous asteroid abstract based on the reflectance spectra surface materials of many c g b and f type asteroids are altered by heating and consist of low crystalline dehydrated phyllosilicates similar to heated hydrous carbonaceous chondrites however meteorites of this kind studied so far were not samples from the asteroid regolith but from the asteroid interior they lack both of two properties characteristic for regolith materials lithologies with impact induced brecciation and noble gases from implanted solar winds thus no meteorite samples have ever been identified as a real sample of c g b and f type asteroid regolith here i report the discovery of a meteorite having mineralogical and isotopic signatures expected for regolith samples of these asteroids through the investigation of seven cm carbonaceous chondrites the meteorite is the yamato y 793321 cm carbonaceous chondrite it exhibits a variety of petrologic features that are characteristic of active regolith material chondrules are crushed matrix is comminuted and coarse silicate crystals show deformation and characteristic planner fractures due to repeated impacts synchrotron x ray diffraction analysis showed that fine grained matrix is dominated by amorphous silicates with minor amounts of olivine and magnetite which was produced by dehydration of preexisting hydrous phases probably serpentine during impact induced heating at 500 c in addition isotopic analysis revealed that the meteorite is enriched in implanted solar noble gases suggesting that it was once located at surface layers of a parent asteroid all results taken together demonstrate that y 793321 is a regolith breccia of a hydrous asteroid which underwent impacts heating dehydration and solar wind implantation at the surface layers of the asteroid the reflectance spectrum of this meteorite matches well with those of asteroids c g b and f confirming that it was derived from these asteroid surfaces

equivalent number of uniform stress cycles for soil liquefaction analysis the seismic demand on potentially liquefiable soils can be approximated by a series of uniform shear stress cycles procedures are reviewed for converting an arbitrary acceleration time history to a series of uniform cycles with amplitude 0 65 of the peak the number of cycles n at this amplitude is evaluated so as to represent a seismic demand for liquefaction triggering equivalent to that of the accelerogram an assumed relationship between n and magnitude m underlies so called magnitude scaling factors used to adjust the liquefaction resistance of soil for the effects of duration magnitude scaling factors can alternatively be related directly to n which enables the effects of factors other than m for example site source distance r to be quantified we develop empirical models for n that are applicable to active tectonic regions and find a strong dependence on m and r and a weaker dependence on site condition and near fault rupture directivity effects the model for n is used to develop new s

influence of lixiviation by irrigation water on residual shear strength of weathered red mudstone in northwest china implication for its role in landslides reactivation abstract irrigation in loess tableland areas of northwest china has induced a large number of landslides around their edges of which loess red mudstone landslide is one of the most frequent types salt sinters commonly observed at the toes of these landslides where the weathered red mudstone wrm outcrops have raised the possibility that removal of soluble salts in the wrm by irrigation water could be crucial in the reduction of its shear strength and thus in the occurrence of these landslides in order to investigate the effects of lixiviation by irrigation water on residual shear strength of the wrm samples of the wrm close to two landslides in lanzhou city one of the largest cities in northwest china were tested after being treated under different conditions these included 1 saturation with the yellow river water the only source of irrigation 2 saturation with groundwater and 3 saturation and leaching with deionized water based on the results of these tests specific mechanisms of residual shear strength reduction of the wrm due to lixiviation by irrigation water were discussed in terms of physico chemical interactions between the wrm and water it was found that lixiviation reduced residual shear strength and residual friction angle r of the wrm by up to 65 and 62 respectively after being leached 6 times this coincided with a dramatic dissolution and leaching of soluble salts from the wrm particle size distribution showed that the more the wrm was leached the more the clay fraction and the lesser coarser fractions this suggested that reduction in residual shear strength of the wrm could be attributed to mainly disaggregation of particles coarser than clay and to a lesser degree to weakening of interparticle forces among individual clays it was further postulated that variation in clay mineralogy may influence performance of particle disaggregation

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

transmission electron microscopy of concordia ultracarbonaceous antarctic micrometeorites ucamms mineralogical properties we performed mineralogical and petrographic studies of three ultracarbonaceous antarctic micrometeorites ucamms by analytical transmission electron microscopy tem the ucamms were identified in the concordia micrometeorite collection 2002 and 2006 recovered from central antarctic snow and are of probable cometary origin ucamms are dominated by disordered carbonaceous matter that extends over surfaces of up to 90 of the particle embedded in this carbonaceous matter we observed small and complex assemblages of fine grained mineral phases isolated minerals glassy phases that resemble glass with embedded metal and sulfides gems that were first found in interplanetary dust particles idps and rounded objects containing both glass and crystalline materials the mineral assemblages are chondritic in composition within a factor of 2 crystalline materials represent at least 25 of mineral phases this value is much larger than the upper limit of crystallinity measured in the diffuse interstellar medium 2 2 wt crystalline phases are dominated by low ca mg rich pyroxenes mg rich olivine and low ni fe sulfides exotic phases such as mn zn rich sulfide and perryite have also been found as accessory minerals the variety of high temperature mineral phases observed in ucamms is similar to that reported in chondritic porous idps and 81p wild 2 samples the close association of high temperature crystalline phases with the low temperature carbonaceous matter in ucamms supports the hypothesis of a large scale radial mixing in the early solar nebula this new type of carbon rich micrometeorites containing crystalline material provides the opportunity to analyze in situ without any chemical processing the association of materials formed at both low and high temperatures in the protoplanetary disk a better knowledge of these samples is also important to prepare for future cometary missions like rosetta in 2014

geometry and kinematics of a landslide surface in tertiary clays from the duero basin spain abstract the penalba roto translational landslide is one of the large landslides that can be observed in the central area of the duero basin spain its present morphology is a semicircular shaped depression in which more than 6 m of vertical movement have been measured the erosion of the banks of the duero river affecting the slope of the penalba hill has incised vertical cliffs where a slip surface outcrops and can be observed currently the incision level of the duero river is located 22 m below this surface the slip surface on the translational zone within a large roto translational landslide developed within the duenas facies in a single bed with a high pi 39 0 47 8 and lower carbonate contents would have behaved as low shear strength surfaces r 18 21 8 at penalba the slip surface and the deformation structures related to it have been exceptionally well preserved the structures observed are similar to those usually described in shear zones of tectonic origin an s c fabric related to progressive simple shear and c planes called extensional crenulation cleavage these similarities suggest that analogous kinematic processes would have taken place in completely different geodynamic environments in the present work we have adopted a structural geological kinematic approach to explain the development of the features in this roto translational landslide

contrasting subduction structures within the philippine sea plate hydrous oceanic crust and anhydrous volcanic arc crust we show contrasting subduction structures within the philippine sea plate inferred from active source wide angle reflection data previous studies showed that large amplitude reflections from the slab are observed in southwest japan and indicated that a thin low velocity layer with a high fluid content is formed along the top of the subducting oceanic crust on the contrary we found that the slab reflections have smaller amplitudes in the izu collision zone central japan where the izu bonin volcanic arc has been colliding subducting suggesting that such a low velocity layer does not exist beneath the collision zone this structural difference is also supported by p wave and s wave velocity anomalies by passive source tomography and electrical conductivity and correlates with the regional distribution of deep tremors and intraslab earthquakes both of which are induced by dehydration processes within the downgoing slab based on these comparisons we suggest that the original structure of the incoming plate controls the contrasting subducting systems typical oceanic plate absorbs water by hydrothermal circulation at spreading centers and or seawater infiltration at outer rises whereas volcanic arc crust consumes a large amount of hydrous minerals for melt production and metamorphoses to more stable anhydrous forms before subduction

dynamics characteristic of red clay in a deep seated landslide northwest china an experiment study abstract the red mudstone sediments are widely encountered in earthquake region northwestern china which is vulnerable to the occurrence of landslides previous studies focused on rain induced shallow landslides some deep seated landslides in red clay with a gentle inclination are still not well understood a fatal landslide named as zhengjiamo landslide located in tianshui china was investigated the aim of this study was to study mechanism of shear surface development under earthquake using a series of cyclic triaxial tests the test results of the red clay from the zhengjiamo landslide revealed that the undrained shear strength and excess pore pressure increase with increasing confining stresses 3 and ocr it is also observed that those stress strain behaviors on the deviatoric stress axial strain and pore water pressure subsequent to the initial contractive response the saturated clay exhibited dilation upon continued shearing the dilated tendency of the clay becomes more prevalent with increasing confining stresses 3 and ocr during the dynamic response the reduction of shear strength of the red clay is substantially caused by the increasing number of cycles n under earthquakes the sliding zone may behave in a brittle ductile pattern

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