a short lived 26al induced hydrothermal alteration event in the outer solar system constraints from mn cr ages of carbonates abstract a key process in the early solar system that significantly affects the further evolution and transport of highly volatile elements throughout the solar system hydrothermal parent body alteration to determine whether hydrothermal alteration in outer solar system parent bodies occurred more or less simultaneously or due to a sequence of multiple different events we investigated low temperature hydrothermally altered cm and ci chondrites along with volatile rich cm like clasts and c1 clasts with abundant mineral phases that contain volatiles in this respect c1 clasts are particularly important as they closely resemble the ci chondrites but originate from isotopically different parent bodies specifically we applied the sims based mn cr in situ dating technique to carbonates a common hydrothermally formed phase in low temperature hydrothermally altered meteorites the mn cr ages of dolomites in ci chondrites and c1 clasts as well as calcites in cm chondrites and cm like clasts reveal that nearly all carbonates in low temperature hydrothermally altered clasts and chondrites were formed within a brief period between 2 6 ma after cai formation given this sharp separation and that hardly any material contains carbonates formed later than 6 ma after cai formation hydrothermal alteration likely occurred near contemporaneously among different parent bodies in the outer solar system further the timing of hydrothermal alteration matches peak heating of 26al decay that ceased at 5 ma after cai formation hereby these results are consistent with a model in which the carbonates in low temperature hydrothermally altered parent bodies precipitated from the fluid produced by melting ice the results also show that other potential heating events e g impacts only negligibly contributed to creating environments where fluid mediated dissolution and precipitation of carbonates was possible additionally the isotopic h o cr and s differences between c1 clasts and ci chondrites are most likely not caused by differences in timing of hydrothermal aqueous alteration and thus are best explained by spatially different isotopic reservoirs

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

hydrogen isotopic composition of ci and cm like clasts from meteorite breccias sampling unknown sources of carbonaceous chondrite materials abstract volatile rich ci and cm like clasts occur in different brecciated achondrite and chondrite groups the ci like clasts in heds polymict ureilites as well as ordinary cr and cb chondrites have a similar mineralogy indicating a similar alteration history however when viewed in detail their mineral chemistry shows some minor differences between the clasts from different meteorite groups for cm like clasts found in hed meteorites the clasts are based on their mineralogy clearly fragments of cm chondrites to be able to decipher whether ci or cm like clasts from different meteorite groups are related to certain meteorite classes known to contain volatiles we obtained d h ratios of several clasts from the meteorite groups mentioned above and compared them with those of ci and cm chondrites as well as to unique carbonaceous chondrites such as bells essebi and tagish lake considering the d values cm like clasts in heds span a similar range compared to bulk values of cm chondrites further indicating that cm like clasts are fragments of cm chondrites for ci like clasts a clear distinction can be made while ci like clasts in heds and ordinary chondrites show a very similar range in their d signatures compared to common ci chondrites meaning that these clasts are likely related to ci chondrites the ci like clasts in polymict ureilites are enriched in d up to 3000 a similarly high enrichment is found for the ci like clasts in cr chondrites thus although the ci like clasts in ureilites and cr chondrites likely experienced similar alteration histories as the ci like clasts found in the other meteorite types these clasts probably formed in a different region than the ci chondrites and thus are more accurately referred to as c1 clasts overall the existence and isotopic signatures of the c1 clasts in several meteorite groups proves the existence of additional primitive volatile rich material in the early solar system besides the matter we study as the ci cm and cr chondrites this material was distributed throughout the solar system very early and might have played an important role for the volatile inventory of the terrestrial planets

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

noble gases in individual l chondritic micrometeorites preserved in an ordovician limestone we have measured the he and ne concentrations and isotopic ratios of individual sediment dispersed extraterrestrial chromite grains 63 180 mu m in diameter from an ordovician limestone in southern sweden in the same sediment many fossil meteorites were found and have been attributed to the l chondrite parent body breakup event similar to 470 ma ago in this analysis of 37 individual extraterrestrial chromite grains of l chondritic major element composition at least 35 similar to 95 contain surface implanted helium and neon of fractionated solar wind composition implying that these grains are relict parts of fossil micrometeorites of asteroidal origin similar to what has been observed in recent micrometeorites collected in the polar regions significant amounts of cosmogenic ne 21 were found in several grains resulting in cosmic ray exposure cre ages of up to similar to 77 myr these ages exceed both dynamical lifetimes for asteroidal micrometeorites of this size as well as cre ages observed in chromites from fossil meteorites from the same sediment beds significant contributions from terrestrial sources like nucleogenic and cosmic ray muon induced ne 21 can be excluded in the extraterrestrial chromites since 11 terrestrial chrome spinel grains from the same sediment beds did not contain any measurable ne 21 excesses having found micrometeorites of undisputed asteroidal origin with cosmic ray exposure ages of several 10 7 years implies that high cosmic ray exposure ages alone are not a good indicator of cometary origin in opposition to what has been suggested for recent micrometeorites and idps we propose instead that these grains collected their cosmogenic ne 21 while residing in the regolith layer of their parent body c 2009 elsevier b v all rights reserved less

bed by bed fold growth by kink band migration sant llorenc de morunys eastern pyrenees ahstract rowth strata deposited over and against the flank of the sant llorenc de morunys fold during its final stages of deformation have been mapped at high resolution as the basis for unraveling the kinematics of fold growth we use restoration techniques based on normal balancing assumptions to decipher the detailed kinematic history of folding the progressive restorations as well as balanced forward modeling show that the last few hundred meters of fold growth were dominated by kink band migration of a sort that is typical of much faultrelated folding the kink band migration has produced complex anticlinal hinge zone geometry including segmented fold hinges linked by disconformities and unconformities which has direct and detailed explanation in terms of fluctuations in deposition rate relative to curved hinge kink band migration rate large fluctuations in the convolution of non steady sedimentation and deformation are demonstrated although the absolute fluctuations in deformation and sedimentation are unknown at a length scale of 100 m kink band migration with little or no deposition is interspersed with sedimentation with little or no deformation at the length scale of 500 m deposition ranges from 200 to 50 of uplift 0 1997 elsevier science ltd all rights reserved

ci chondrite like clasts in the nilpena polymict ureilite implications for aqueous alteration processes in ci chondrites abstract we have carried out a detailed petrographic and mineralogical study of carbonaceous chondrite matrix clasts in the nilpena polymict ureilite the bulk compositions of a number of clasts determined by electron microprobe show that they have close affinities to ci chondrite matrix and differ substantially from cm matrix material transmission electron microscopy studies show that the mineralogy of the clasts is also consistent with ci chondrite matrix indicated by the presence of saponitic smectite clays serpentine magnetite pentlandite pyrrhotite and ferrihydrite phases such as tochilinite and cronstedtite diagnostic of cm matrix are absent based on the oxygen isotopic composition of the matrix the phase chemistry and the bulk clast chemistry we suggest that the matrix clasts in nilpena represent material which is less altered than orgueil the difference in oxygen isotopic composition of the nilpena matrix clasts from ci chondrites may be because the clasts underwent alteration at a lower water rock ratio increased alteration of nilpena type material should result in the oxidation of fe bearing saponite and sulfides to produce ferrihydrite and more mg rich saponite such as that in orgueil matrix although the presence of ci like matrix clasts in the polymict ureilites suggests that ci matrix may have been a precursor to the ureilites in detail this seems highly unlikely the trace element and carbon isotopic compositions of ureilites are incompatible with a significant ci chondrite precursor we suggest that the ci like matrix clasts in nilpena represent a component of a late accreting veneer on the ureilite parent body

an exotic kind of cosmic material graphite containing xenoliths from the krymka ll3 1 chondrite abstract seven graphite containing xenoliths were found in the krymka ll3 1 chondrite the xenoliths have the following chemical and mineralogical characteristics which distinguish them from the krymka host 1 low totals in bulk chemical analyses obtained by electron microprobe 2 high bulk fe abundances 3 a uniform recrystallized chondrule free texture 4 the presence of euhedral graphite and carbon rich material 5 higher quantities of troilite and metal 6 a relatively homogeneous composition of silicates 7 a distinctive composition of metal chromite and phosphate 8 isotopically heavy c in graphite compared to both bulk krymka and graphite in other ordinary chondrites the xenoliths are mineralogically similar but not identical to the krymka carbonaceous clast k1 which bears graphite microcrystals organic compounds and mysterite they resemble carbonaceous chondrites both chemically and isotopically the mineralogical chemical and isotopic data for the graphite containing fragments suggest that this material represents metamorphosed varieties of a previously unknown type of unequilibrated carbonaceous matter most likely the graphite has a metamorphic origin and was crystallized from c containing precursor materials through the following transformation sequence organic compounds c rich material graphite

kinematics and a balanced and restored cross section across the toe of the eastern nankai accretionary prism abstract seismic profiles across the eastern nankai accretionary prism show evidence for diffuse deformation through stratal thickening and uplift of the accreting sediment package thought to reflect the combination of small scale ductile and brittle strains evident within drill cores using a kinematic solution based on changes in stratal thickness and porosities diffuse strains are estimated for a transect across the eastern nankai accretionary prism toe in the vicinity of odp site 808 calculated element displacements are used to reconstruct the undeformed configuration of the prism toe providing a new method for balancing and restoring deformation in accretionary prisms the results of this analysis demonstrate a heterogeneous distribution of strain within the prism toe which appears to correlate with the distribution of brittle deformation structures in drill cores the greatest vertical tectonic thickening and horizontal shortening estimates are obtained within the deepest sediments which also display abundant brittle shears shallower sediments exhibit high volume loss and lower horizontal shortening and in drill cores display very few deformation structures this spatially variable strain distribution may result from inferred high pore pressures near the frontal thrust and decollement inducing a brittle overprint of previous ductile strains

penecontemporaneous metamorphism fragmentation and reassembly of ordinary chondrite parent bodies the occurrence and proportions of petrologic types among ordinary chondrites have been explained by internal heating of three h l ll parent asteroids of 100 km radius e g miyamoto et al 1982 this conventional onion shell model predicts an inverse relation between petrologic type and metallographic cooling rate but none has been observed scott and rajan 1981 devised a metamorphosed planetesimal model to explain this discrepancy whereby metamorphism occurs in planetesimals a few kilometers in radius which then accrete to form r 100 km parent bodies metallographic cooling rates are then controlled by burial depth thermal and collisional constraints on the metamorphosed planetesimal model are examined here and the model is found to be applicable only to highly insulating 26al rich planetesimals that can accrete intact without being shattered by impact or to shattered planetesimals whose fragments are not widely dispersed over the target surface an alternative model is presented here in which onion shell parent bodies are collisionally fragmented during metamorphism and then gravitationally reassembled if reassembly times are short days then metallographic cooling rates would be determined by burial depth in the reaccreted parent body this model unlike previous ones can explain both coherent and incoherent cooling rates of breccia clasts by collisions during or after metamorphism respectively

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

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

expected characteristics of cometary meteorites recent developments in our understanding of comets provide insights into the topic of cometary meteorites these developments include the identification of comet asteroid transition objects such as 4015 wilson harrington and 3200 phaethon information on the composition of cometary solids and new ideas on the collisional history of jupiter family comets in this work we revisit this question and we conclude that comets do indeed yield macroscopic meteorites which either have not been found or have not been recognized we also consider the expected characteristics of cometary meteorites with an emphasis on those that may help identify and differentiate them from other types of meteorites if cometary meteorites have preserved the main characteristics of cometary dust the mineralogy would be dominated by highly unequilibrated anhydrous silicates and the chemistry would be nearly chondritic but with a high abundance of c and n on the other hand if an unknown process produced extensive aqueous alteration in the material that formed cometary meteorites they would resemble or could even be ci carbonaceous chondrites we do not expect cometary meteorites to have chondrules so far no single meteorite looks unequivocally cometary however we have identified xenoliths in ordinary chondrite regolith breccias that meet most of our criteria for a cometary origin and deserve further study

progressive evolution of a fault related fold pair from growth strata geometries sant llorenc de morunys se pyrenees abstract new structural stratigraphical mapping constrains the three dimensional kinematics and mechanisms of eocene oligocene growth folding at sant llorenc de morunys ne ebro basin spain a 1 km wide sub vertical panel of syntectonic alluvial gravels passes southwards via a highly asymmetrical growth fold pair to shallowlydipping strata the axial surface of the anticline comprises either continuous or en echelon segments while that of the syncline is concave and usually continuous while converging upwards the axial surfaces do not define growth triangles principal and subsidiary growth unconformities and thickness changes occur across both axial surfaces and the common limb dips within the common limb decrease up stratigraphy and up dip mesostructures indicate that internal deformation was ongoing during folding at all stratigraphical levels and concentration of cleavage in the syncline indicates that this hinge was essentially fixed sequential restoration of three profiles shows that folds amplified principally by limb rotation but incorporated minor passive hinge migration particle movement vectors generated by section restoration are arcuate about a hinterland pinpoint a new trishear model of fault propagation folding involving non rigid limb rotation reproduces the rounded hinge forms thickening geometries and limb dip variations observed simple kink band migration models fixed axis and constant thickness theories do not replicate these features

nature of the h chondrite parent body regolith evidence from the dimmitt breccia the dimmitt h chondrite regolith breccia consists of in vol 40 h4 and h5 chondrite clasts 3 impact melt rock clasts 0 5 shocked h chondrite clasts 1 5 exotic clasts including carbonaceous and ll5 chondrites and 55 gas rich matrix the ll5 clast is the best documented example of an ordinary chondrite in a host of a different compositional group the matrix contains unequilibrated material which differs from typical h3 material in having little 0 2 vol fine grained opaque silicate matrix and having 20 of the olivines with compositions in the range fa21 24 about 10 15 of this unequilibrated material is probably derived from graphite magnetite rich chondrites and 2 from h3 0 3 5 chondrites the absence of h3 clasts suggests that most of the unequilibrated material was derived from unconsolidated type 3 components many exotic clasts may have been derived from planetesimals that accreted to the h chondrite parent body prior to regolith development one slowly cooled melt rock clast formed beneath a 500 m thick melt breccia pile on the floor of a large impact crater and was later excavated by additional impacts incorporated into the regolith and consolidated with other components to form the dimmitt breccia

heavily hydrated lithic clasts in ch chondrites and the related metal rich chondrites queen alexandra range 94411 and hammadah al hamra 237 fine grained heavily hydrated lithic clasts in the metal rich cb chondrites queen alexandra range que 94411 and hammadah al hamra 237 and ch chondrites such as patuxent range pat 91546 and allan hills alh 85085 are mineralogically similar suggesting genetic relationship between these meteorites these clasts contain no anhydrous silicates and consist of framboidal and platelet magnetite prismatic sulfides pentlandite and pyrrhotite and fe mn mg bearing ca carbonates set in a phyllosilicate rich matrix two types of phyllosilicates were identified serpentine with basal spacing of similar to0 73 nm and saponite with basal spacings of about 1 1 1 2 nm chondrules and feni metal grains in cb and ch chondrites are believed to have formed at high temperature 1300 k by condensation in a solar nebula region that experienced complete vaporization the absence of aqueous alteration of chondrules and metal grains in cb and ch chondrites indicates that the clasts experienced hydration in an asteroidal setting prior to incorporation into the ch and cb parent bodies the hydrated clasts were either incorporated during regolith gardening or accreted together with chondrules and feni metal gains after these high temperature components had been transported from their hot formation region to a much colder region of the solar nebula

three dimensional architecture of growth strata associated to fault bend fault propagation and decollement anticlines in non erosional environments abstract the evolution of surficial structures at the toes of orogens arises from the complex interplay between tectonic and surface processes the internal architecture of syntectonic sediments has been shown to provide useful insights on the kinematic mechanism of folding two dimensional templates of growth strata patterns associated to thrust related anticlines are available in the literature in this paper we show the results of three dimensional numerical modelling of growth fault bend folds fault propagation folds fixed limb length decollement folds and fixed limb dip decollement folds we point out that total thickness contour maps single syntectonic layer contour maps and above all the computation of their directional first derivative maps provide useful templates for inferring the kinematic mechanism of folding when compared with similar maps from natural examples application of these three dimensional numerical models includes the comparison and supervised best fit with three dimensional seismic reflection data sets numerical results are contrasted with the growth strata map patterns of the mediano oliana and pico del aguila anticlines in the spanish pyrenees

the genesis of diogenites and hed parent body petrogenesis abstract samples of clasts and whole rocks from eighteen of the twenty four known diogenites orthopyroxenite breccia meteorites have been studied by combined inaa empa in order to elucidate their petrogenetic history the incompatible elements a12o3 and tio2 are positively correlated in diogenite orthopyroxenes these elements determined by empa are also positively correlated with incompatible trace elements such as yb determined by inaa on bulk samples these correlations indicate that most diogenites may form a single igneous fractionation sequence the incompatible minor and trace elements are decoupled from the major elements for essentially constant mg tio2 varies by about 4 times and yb by about 8 times hence there is no strong evidence for igneous fractionation preserved in the major element composition of orthopyroxenes geothermometry calculations using two pyroxene and spinelorthopyroxene thermometers show that these phases in diogenites maintained equilibrium to temperatures in the range 650 880 c far below likely magmatic temperatures in some diogenites orthopyroxenes of differing composition are in breccia contact therefore the low equilibration temperatures were achieved in the diogenites prior to brecciation decoupling of major and trace elements was most likely caused by slow subsolidus cooling in the diogenite pluton which allowed ca fe and mg to reach diffusive equilibration incompatible trace elements likely have much lower diffusivities in orthopyroxene and therefore may have largely preserved their magmatic distributions the extensive variation in incompatible trace elements indicates that either the diogenites were formed through an extensive crystallization interval or that partition coefficients greatly increased during crystallization if the former were true one would expect to find substantial amounts of plagioclase in the diogenites if they are comagmatic with eucrites this is contrary to observations a model in which diogenites crystallized from one or more melts of approximately orthopyroxenitic composition can satisfy both the mineralogie and trace element constraints

numerical modeling of trishear fault propagation folding in contrast to kink band migration modeling methods trishear numerical models produce fault propagation folds with smooth profiles and rounded hinges modeled fold hinges tighten and converge downward within a triangular zone of distributed deformation which is focused on the fault tip such features have been reported from field studies and are also seen in analogue models of compressional deformation however apart from its initial application to laramide folds little quantitative work has been undertaken on trishear fault propagation folding in other settings in addition no study has been undertaken into the growth strata which might be associated with such structures this paper uses an equivalent velocity description of the geometric model of trishear together with models of erosion and sedimentation to investigate trishear fault propagation folding of both pregrowth and growth strata the trishear model is generalized to include a variety of fault propagation to slip ratios and fault propagation from a flat decollement the models show continuous rotation of the forelimb with the characteristic development of cumulative wedges within growth strata when total slip on a structure is high the model predicts overturned pregrowth and growth strata during the initial stages of deformation beds in the forelimb thicken but later thin when they become steep or overturned the effect of variations in fault propagation to slip ratios on two dimensional finite strain in the models is assessed by the use of initially circular strain markers high fault propagation to slip p s ratios lead to narrow zones of high finite strain while lower p s ratios lead to more ductile deformation and broader zones of high strain in all cases hanging wall anticlines and footwall synclines originate as early ductile folds which are later cut by the propagating fault modeled structures are compared with natural examples

the gao guenie impact melt breccia sampling a rapidly cooled impact melt dike on an h chondrite asteroid the gao guenie h5 chondrite that fell on burkina faso march 1960 has portions that were impact melted on an h chondrite asteroid at 300 ma and through later impact events in space sent into an earth crossing orbit this article presents a petrographic and electron microprobe analysis of a representative sample of the gao guenie impact melt breccia consisting of a chondritic clast domain quenched melt in contact with chondritic clasts and an igneous textured impact melt domain olivine is predominantly fo80 82 the clast domain contains low ca pyroxene impact melt grown pyroxene is commonly zoned from low ca pyroxene in cores to pigeonite and augite in rims metal troilite orbs in the impact melt domain measure up to 2 mm across the cores of metal orbs in the impact melt domain contain 7 9 wt of ni and are typically surrounded by taenite and ni rich troilite the metallography of metal troilite droplets suggest a stage i cooling rate of order 10 c s 1 for the superheated impact melt the subsolidus stage ii cooling rate for the impact melt breccia could not be determined directly but was presumably fast an analogy between the ni rim gradients in metal of the gao guenie impact melt breccia and the impact melted h6 chondrite orvinio suggests similar cooling rates probably on the order of 5000 40 000 c yr 1 a simple model of conductive heat transfer shows that the gao guenie impact melt breccia may have formed in a melt injection dike 0 5 5 m in width generated during a sizeable impact event on the h chondrite parent asteroid

xenoliths and microxenoliths in h chondrites sampling the zodiacal cloud in the asteroid main belt abstract xenoliths are inclusions of a given meteorite group embedded in host meteorites of a different group xenoliths with dimensions between a few m and about 1 mm microxenoliths are meteorite trapped analogues of micrometeorites collected on the earth however they have the unique features of sampling the zodiacal cloud 1 at more ancient times than those sampled by micrometeorites and 2 at larger distances from the sun corresponding to the asteroid main belt than that sampled by micrometeorites 1 au herein we describe a systematic search for new xenoliths and microxenoliths in h chondrites aimed at determining their abundance in these ordinary chondrites analyzing their mineralogy and searching for possible correlations with host meteorite properties sixty six sections from 40 meteorites have been analyzed twenty four new xenoliths have been discovered about 87 of them are microxenoliths i e 1 mm in their largest dimension all the newly discovered xenoliths and microxenoliths are composed of carbonaceous chondritic material hence the zodiacal cloud was dominated by carbonaceous material even in past epochs all the new xenoliths and microxenoliths have been found in regolith breccias hydrous phase rich xenoliths and microxenoliths in h4 and h5 chondrites attest that their embedding happened after the end of the thermal metamorphism all these data suggest that xenoliths and microxenoliths were embedded when their host meteorites were part of the parent body regolith this combined with the h chondrite impact age distribution attests that the embedding may have happened as early as 3 5 gyr ago

microchondrule bearing clast in the piancaldoli ll3 meteorite a new kind of type 3 chondrite and its relevance to the history of chondrules in the piancaldoli ll3 chondrite we found a mm sized clast containing 100 chondrules 0 2 64 m in apparent diameter much smaller than any previously reported that are all of the same textural type radial pyroxene fs1 17 this clast like other type 3 chondrites has a fine grained ferich opaque silicate matrix sharply defined chondrules abundant low ca clinopyroxene and minor troilite and si and cr bearing metallic fe ni however the very high modal matrix abundance 63 8 vol unique characteristics of the chondrules and absence of microscopically observable olivine indicate that the clast is a new kind of type 3 chondrite most chondrules have feo rich edges and chondrule size is inversely correlated with chondrule core feo concentration the first reported correlation of chondrule size and composition chondrules acquired fe by diffusion from fe rich matrix material during mild metamorphism possibly before final consolidation of the rock microchondrules those chondrules 100 m in diameter are also abundant in another new kind of type 3 chondrite clast in the rio negro l chondrite regolith breccia in other type 3 chondrite groups microchondrule abundance appears to be anticorrelated with mean chondrule size viz 0 02 0 04 vol in h and co chondrites and 0 006 vol in l ll and cv chondrites microchondrules probably formed by the same process that formed normal sized droplet chondrules melting of pre existing dustballs because most compound chondrules in the clast and other type 3 chondrites formed by collisions between chondrules of the same textural type we suggest that dust grains were mineralogically sorted in the nebula before aggregating into dustballs the sizes of compound chondrules and chondrule craters which resulted from collisions of similarly sized chondrules while they were plastic indicate that size sorting of dustballs occurred before chondrule formation probably by aerodynamic processes in the nebula we predict that other kinds of type 3 chondrites exist which contain chondrule abundances size ranges and proportions of textural types different from known chondrite groups

early solar system processes recorded in the matrices of two highly pristine cr3 carbonaceous chondrites met 00426 and que 99177 the mineralogy and bulk compositions of the matrices of the cr chondrites met 00426 and que 99177 have been studied using a combination of sem epma and tem techniques the matrices of these two chondrites are texturally chemically and mineralogically similar and are characterized by significant feo enrichments with respect to other cr chondrite matrices nearly flat refractory lithophile patterns variable volatile element patterns and a simple mineral assemblage dominated by amorphous silicate material and fe ni sulfides fine grained crystalline silicate phases such as olivine and pyroxene appear to be extremely rare in the matrices of both meteorites instead the mineralogy of matrices and fine grained rims of both meteorites consists of abundant amorphous feo rich silicate material containing nanoparticles of fe ni sulfides troilite pyrrhotite and pentlandite secondary alteration minerals that are characteristic of other cr chondrites e g renazzo and al rais such as phyllosilicates magnetite and calcite are also rare the texture and mineralogy of the matrices of met 00426 and que 99177 share many features with matrices in the primitive carbonaceous chondrites alh a77307 co3 0 and acfer 094 unique these observations show that met 00426 and que 99177 are very low petrologic type 3 chondrites that have escaped the effects of aqueous alteration unlike other cr chondrites which are typically classified as petrologic type 2 we suggest that these meteorites represent additional samples of highly primitive but extremely rare carbonaceous chondrites of petrologic type 3 00 according to the classification scheme of grossman and brearley 2005 the highly pristine nature of met 00426 and que 99177 provides important additional insights into the origins of fine grained materials in carbonaceous chondrites based on our new observations we infer that the amorphous silicate material and nanosulfide particles that dominate the matrices of these meteorites formed in the solar nebula by rapid condensation of material following high temperature events such as those that formed chondrules

hydrogen isotopic composition of water from fossil micrometeorites in howardites we have measured the hydrogen isotopic composition d h ratios of the water from 13 carbonaceous chondritic microclasts ccms size 1 mm trapped in two howardites kapoeta and yamato 793497 early in the evolution of solar system the division into tochilinite rich magnetite rich olivine poor magnetite rich olivine rich ccm types is corroborated by the hydrogen isotopic compositions both mineralogy and hydrogen isotopic compositions demonstrate that tochilinite rich ccms represent cm2 chondritic matter in contrast there is no good match between the isotopic and mineralogical properties of the magnetite rich ccms and the known groups of carbonaceous chondrites suggesting that magnetite rich ccms represent a new kind of chondritic matter not yet sampled in meteorite collections this demonstrates that the view of the asteroid belt revealed by the collection of meteorites is incomplete the study of micro clasts offers a unique opportunity to better decipher the nature and relative abundance of asteroids the average hydrogen isotopic composition of water belonging to ccms d h 152 0 4 8 x 10 6 1 sigma m is similar to that of antarctic micrometeorites amms d h 161 2 3 8 x 10 6 1 sigma m the similarity in terms of mineralogy and hydrogen isotopic composition between ccms and amms demonstrates that the composition of the micrometeorites has not been modified over the whole history of the solar system it indicates that the composition of the micrometeorite flux onto earth has been and is dominated by a mixture of cm2 like magnetite rich olivine poor magnetite rich olivine rich carbonaceous chondritic matter exemplified by ccms found in howardites because ccms have not suffered atmospheric entry they provide an abundant source of pristine micrometeorites the average d h ratio of the whole population of ccms is identical within errors to that of the earth 149 3 x 10 6 the match between the ccms d h ratio and that of the earth is especially remarkable because 1 three different populations of ccms are needed to make the d h ratio of the earth 2 there is no single carbonaceous chondrite group for which a similar match exists this observation suggests that ccms population might be representative of the late veneer agent s that delivered water to the earth

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

regolith migration and sorting on asteroid itokawa high resolution images of the surface of asteroid itokawa from the hayabusa mission reveal it to be covered with unconsolidated millimeter sized and larger gravels locations and morphologic characteristics of this gravel indicate that itokawa has experienced considerable vibrations which have triggered global scale granular processes in its dry vacuum microgravity environment these processes likely include granular convection landslide like granular migrations and particle sorting resulting in the segregation of the fine gravels into areas of potential lows granular processes become major resurfacing processes because of itokawa s small size implying that they can occur on other small asteroids should those have regolith

the matrices of unequilibrated ordinary chondrites implications for the origin and history of chondrites abstract the matrices of sixteen unequilibrated ordinary chondrites all witnessed falls were studied microscopically in transmitted and reflected light and analyzed by electron microprobe selected specimens were also studied by scanning electron microscopy these studies indicate that the fine grained opaque silicate matrix of type 3 unequilibrated chondrites is compositionally mineralogically and texturally distinct from the chondrules and chondrule fragments and may be the low temperature condensate proposed by larimer and anders 1967 1970 examination of the matrices of unequilibrated chondrites also shows that each meteorite has been metamorphosed with the alteration ranging in intensity from quite mild where the matrix has been only slightly altered to a more severe metamorphism that has completely recrystallized the opaque matrix most of the metamorphic changes in the matrix occurred without significant effects on the compositions or textures of the chondrules the metamorphic alteration probably resulted from a combination of processes including thermal metamorphism and the passage of shock waves the present appearance of each unequilibrated chondrite is a result of the particular temperature and pressure conditions under which it and its components formed plus the subsequent metamorphic alteration it experienced

shock metamorphism of ordinary chondrites a revised petrographic classification of progressive stages of shock metamorphism of ordinary chondrites is proposed six stages of shock s1 to s6 are defined based on shock effects in olivine and plagioclase as recognized by thin section microscopy the characteristic shock effects of each shock stage are s1 unshocked sharp optical extinction of olivine s2 very weakly shocked undulatory extinction of olivine s3 weakly shocked planar fractures in olivine s4 moderately shocked mosaicism in olivine s5 strongly shocked isotropization of plagioclase maskelynite and planar deformation features in olivine and s6 very strongly shocked recrystallization of olivine sometimes combined with phase transformations ringwoodite and or phases produced by dissociation reactions s6 effects are always restricted to regions adjacent to melted portions of a sample which is otherwise only strongly shocked in stages s3 to s6 localized melting results from stress and temperature peaks which locally deviate from the equilibration shock pressure due to differences in shock impedance these melting effects are a opaque melt veins shock veins b melt pockets with interconnecting melt veins c melt dikes and d troilite metal deposits in fractures based on a critical evaluation of data from shock recovery experiments a shock pressure calibration for the six shock stages is proposed which defines the s1 s2 s2 s3 s3 s4 s4 s5 and s5 s6 transitions at 5 5 10 15 20 30 35 and 45 55 gpa respectively whole rock melting and formation of impact melt rocks or melt breccias occurs at about 75 90 gpa the symbol for the shock stage may be used in combination with the symbol for the petrologic type to abbreviate the complete classification of a chondrite e g h5 s3 we propose this new shock classification and pressure calibration system to replace previous systems which are out of date with respect to the pressure calibration nominally restricted to l chondrites and based on incomplete and in part illdefined sets of shock effects we have classified seventy six ordinary chondrites using the new classification system and conclude the following 1 1 shock effects and the sequence of progressively increasing degrees of shock metamorphism are very similar in h l and ll groups differences in the frequency distribution of shock stages are relatively minor e g l chondrites appear to have the largest fraction with stages s5 and s6 this suggests that the collisional histories of the h l and ll parent bodies were similar 2 2 petrologic type 3 chondrites are deficient in stages s4 to s6 and with increasing petrologic type the frequency of stages s4 to s6 increases we suggest that the more porous and volatile rich type 3 chondrites are subject to melting at a lower shock pressure than the nonporous chondrites of higher petrologic type volatiles trapped in pores cause shock induced dispersal of the shocked and melted material into small particles which are not expected to survive as meteorites 3 3 stage s3 is the most abundant in nearly all petrologic types 4 4 at shock pressures in excess of about 35 gpa s5 and s6 4he and 40ar are almost completely lost pressures below 10 gpa s1 and s2 do not cause noble gas losses

weakly shocked and deformed cm microxenoliths in the pultusk h chondrite the pultusk meteorite is a brecciated h4 5 chondrite cut by darkened cataclastic zones within the breccia relict type ia ib and iia chondrules and microxenoliths of carbonaceous cm chondrite lithology occur this is the first description of foreign clasts in the pultusk meteorite the matrix of the xenoliths was identified by usage of microprobe and raman spectroscopic analyses raman spectra show distinct bands related to the presence of slightly ordered carbonaceous matter at approximately 1320 and 1580 1584 cm 1 bands related to serpentine group minerals are also visible especially a peak at 692 cm 1 and moreover other weak bands are interpreted as evidence for tochilinite we decipher the metamorphic and deformational history of the xenoliths they experienced aqueous alteration before being incorporated into the unaltered and well equilibrated parent rock of the pultusk chondrite the xenoliths are weakly shocked as indicated by defects in the crystal structure of silicates and carbonates but hydrated minerals serpentine and tochilinite are still present in the matrix the carbonaceous matter within the clasts matrix displays first order d and g raman bands that suggests it is only slightly ordered as a result of mild thermal processing distinct shear bands are present in both the xenoliths and the surrounding rock which testifies that the xenoliths were affected by a deformational event along with host rock the host rock was brittly deformed but the clasts experienced more ductile deformation revealed by semibrittle faulting of minerals kinking of the tochilinite cronstedtite matrix and injections of xenolithic material into the adjacent breccia we argue that both processes the high strain rate shear deformation and the incorporation of the xenoliths into the host pultusk breccia could have been impact related the pultusk xenoliths are thus rather spalled collisional fragments than trapped fossil micrometeorites

a kinematic model for the origin of footwall synclines abstract the origin of footwall synclines at the base of thrust ramps can be related to the kinematic evolution of fault propagation folds the conventional fault propagation fold model does not predict the development of footwall synclines because it assumes a high propagation to slip ratio for development of the lower flat which does not allow for folding before the thrust cuts up section an alternative model where the propagation to slip ratio remains finite throughout the development of the fault propagation fold produces a detachment fold at the thrust tip during propagation of the thrust along the lower flat if the thrust cuts up through the ductile core of the detachment fold during ramp formation it will leave behind the forelimb of the detachment fold as part of a footwall syncline

carbonate compositions in cm and ci chondrites and implications for aqueous alteration abstract carbonate minerals in fourteen cm chondrites and two ci chondrites have been analyzed by electron microprobe to provide a better understanding of the aqueous processes that affected carbonaceous chondrite parent bodies calcites in cm chondrites and dolomites and magnesites in ci chondrites display the compositions expected of stable phases formed at low temperatures dolomites in cm chondrites identified here for the first time in five members of the group have small amounts of excess ca which may reflect metastable growth the distribution of fe between dolomite and coexisting serpentine differs in the two chondrite groups if the distributions reflect an approach to chemical equilibrium then the difference implies higher alteration temperatures for the ci group than the cm group in agreement with the results of previously published oxygen isotope thermometry and mineral solubility modeling of the alteration process dolomite fe contents are relatively uniform in the two chondrite groups dolomite mn contents by contrast vary widely the variations may reflect transport controlled coprecipitation of mn resulting from a heterogeneous distribution of the element in the anhydrous precursor material if this interpretation is correct then the altering fluids were essentially immobile while hydration reactions proceeded on the meteorite parent bodies the near closed system character of the alteration process long known from bulk chemical analyses of the meteorites is a direct consequence of the limited mobility of dissolved species

a conceptual model for the preservation of thick transgressive shoreline successions examples from the forearc nanaimo basin british columbia canada abstract sequence stratigraphic models derived from passive margins and foreland basins characterize transgressive shorelines excluding incised valleys as recording periods of sediment starvation and are commonly represented as thin 10 m are more likely to be developed in active tectonic settings e g forearc and rift basins which generally experience high sedimentation rates and relatively rapid changes in base level settings with high sedimentation rates and moderate base level rise lead to progradational trends despite overall transgression of the shoreline in settings where changes in eustatic sea level mainly control the resulting stratigraphic architecture e g passive margins thin transgressive successions 1 10 m are more likely to be produced finally in settings defined by relatively slow base level change e g foreland basins the resultant transgressive succession typically comprises a lag 1 m overlain by offshore mudstones this conceptual model highlights the importance of the interplay between sedimentation rates and base level rise and is intended as a guide for the predictive modeling of sedimentary basins

formation history of ci like phyllosilicate rich clasts in the tsukuba meteorite inferred from mineralogy and noble gas signatures abstract fine grained angular black clasts with longest dimensions up to 800 m were found dispersed in a brecciated region in the tsukuba meteorite the clasts much darker than the dark portions of the light dark structure in the tsukuba host are characterized by the presence of plaquette spherulitic and framboidal magnetites and pseudo hexagonal pyrrhotite synchrotron radiation x ray diffraction analyses showed that the major silicate phases in the clasts are saponite and serpentine transmission electron microscopy tem revealed that the phyllosilicates have compositions quite similar to those in the orgueil ci carbonaceous chondrite therefore mineralogically and chemically the clasts resemble ci chondrites and are quite different from the host h5 6 chondrite tsukuba the clasts serve as an indicator of temperatures during regolith lithification of the tsukuba parent body because their mineralogy and noble gas compositions are subject to change during weak heating the 001 basal spacing of saponite in the clast is 13 2 a which indicates that saponite retains interlayer water molecules this observation and the presence of serpentine suggest that the clasts as a whole have never been heated above 500 c noble gas analyses showed that the clasts contain large amounts of solar and primordial noble gases the results of stepwise heating analyses indicate that no apparent thermal loss of noble gases from the clasts occurred consistent with the mineralogical evidence tem observation revealed that the periphery of a clast was transformed into amorphous phases indicating that only the periphery was heated to 700 c based on the results of our analyses the formation history of the clasts can be evaluated as follows constituents of the clasts had been exposed to solar wind on the surface of the ci chondrite like parent body and formed the clasts after ejection from the ci like parent body the ci like meteoroid accreted to the tsukuba parent body after early thermal metamorphism that reached 700 1000 c the clasts must have been located in the regolith because they were found among the light dark structure in the meteorite and contain abundant solar noble gases impacts into the regolith have crushed the clasts into smaller pieces and probably induced lithification of the regolith material during lithification the peripheries of the clasts were heated briefly to 700 c but the temperature of the interior of the clasts has never exceeded 500 c this is the first evidence constraining temperature during lithification of the ordinary chondrite parent body regolith finally the tsukuba meteoroid including the ci like clasts was ejected from the tsukuba parent body and fell onto the earth after a transit time of 8 1 ma

geometries of syntectonic sediments associated with single layer detachment folds abstract three kinematic models have been proposed to account for the geometry and kinematics of detachment folds involving a homogeneous competent layer detached over a ductile unit model 1 variable limb dip constant limb length model 2 constant limb dip variable limb length and model 3 variable limb dip variable limb length because the same fold shape can be generated by any of the above mechanisms fold kinematics are best determined by the geometries of syntectonic sediments in single layer detachment folds growth strata patterns are controlled by axial surface activity limb rotation limb lengthening fold uplift rates sedimentation rates and deformation mechanisms of the syntectonic sediments asymmetric kink folds have been modelled and compared with natural examples from the southern spanish pyrenees under conditions of high sedimentation rates model 1 folds produce characteristic fanning growth stratal wedges that initially onlap and then progressively overlap the detachment anticline whereas at low sedimentation rates anticlines with fanning growth wedges on both limbs are formed model 2 folds under conditions of high syntectonic sedimentation rates form anticlines with growth strata largely parallel to the pre growth units and thinned over the fold crest in contrast at low sedimentation rates model 2 folds show offlapping growth strata onto both limbs model 3 growth folds under conditions of high syntectonic sedimentation rates form anticlines with intermediate features from model 1 and model 2 at low sedimentation rates anticlines are formed with offlapping growth structures

evidence for an asteroid comet continuum from simulations of carbonaceous microxenolith dynamical evolution abstract micrometeoroids with 100 and 200 m size dominate the zodiacal cloud dust such samples can be studied as micrometeorites after their passage through the earth atmosphere or as microxenoliths i e submillimetric meteorite inclusions microxenoliths are samples of the zodiacal cloud dust present in the asteroid main belt hundreds of millions years ago carbonaceous microxenoliths represent the majority of observed microxenoliths they have been studied in detail in howardites and h chondrites we investigate the role of carbonaceous asteroids and jupiter family comets as carbonaceous microxenolith parent bodies the probability of low velocity collisions of asteroidal and cometary micrometeoroids with selected asteroids is computed starting from the micrometeoroid steady state orbital distributions obtained by dynamical simulations we selected possible parent bodies of howardites vesta and h chondrites hebe flora eunomia koronis maria as target asteroids estimates of the asteroidal and cometary micrometeoroid mass between 2 and 4 au from the sun are used to compute the micrometeoroid mass influx on each target the results show that all the target asteroids except koronis receive the same amount within the uncertainties of asteroidal and cometary micrometeoroids therefore both these populations should be observed among howardite and h chondrite carbonaceous microxenoliths however this is not the case carbonaceous microxenoliths show differences similar to those existing among different groups of carbonaceous chondrites e g ci cm cr but two sharply distinct populations are not observed our results and the observations can be reconciled assuming the existence of a continuum of mineralogical and chemical properties between carbonaceous asteroids and comets

mineralogy petrography bulk chemical iodine xenon and oxygen isotopic compositions of dark inclusions in the reduced cv3 chondrite efremovka abstract we studied the petrography mineralogy bulk chemical i xe and o isotopic compositions of three dark inclusions e39 e53 and e80 in the reduced cv3 chondrite efremovka they consist of chondrules calcium aluminum rich inclusions cais and fine grained matrix primary minerals in chondrules and cais are pseudomorphed to various degrees by a mixture largely composed of abundant 95 fine grained 0 2 m fayalitic olivine fa35 42 and minor amounts of chlorite poorly crystalline si al rich material and chromite chondrule and cai shapes and textures are well preserved secondary ca rich minerals ti andradite kirschsteinite fe diopside are common in chondrule pseudomorphs and matrices in e39 and e80 the degree of replacement increases from e53 to e39 to e80 fayalitic olivines are heavily strained and contain abundant voids similar to those in incompletely dehydrated phyllosilicates in metamorphosed cm and ci chondrites opaque nodules in chondrules consist of ni and co rich taenite co rich kamacite and wairauite sulfides are rare magnetite is absent bulk o isotopic compositions of e39 and e53 plot in the field of aqueously altered cm chondrites close to the terrestrial fractionation line the more heavily altered e39 is isotopically heavier than the less altered e53 the apparent i xe age of e53 is 5 4 ma earlier than bjurbole and 5 7 2 0 ma earlier than e39 the i xe data are consistent with the most heavily altered dark inclusion e39 having experienced either longer or later alteration than e53 bulk lithophile elements in e39 and e53 most closely match those of co chondrites except that ca is depleted and k and as are enriched both inclusions are depleted in se by factors of 3 5 compared to mean co cv cr or ck chondrites zinc in e39 is lower than the mean of any carbonaceous chondrite groups but in e53 zn is similar to the means in co cv and ck chondrites the efremovka dark inclusions experienced various degrees of aqueous alteration followed by low degree thermal metamorphism in an asteroidal environment these processes resulted in preferential oxidation of fe from opaque nodules and formation of ni and co rich metal metasomatic alteration of primary minerals in chondrules and cais and the formation of fayalitic olivine and secondary ca fe rich minerals based on the observed similarities of the alteration mineralization in the efremovka and allende dark inclusions we infer that the latter may have experienced similar alteration processes

asteroid 2008 tc 3 almahata sitta a spectacular breccia containing many different ureilitic and chondritic lithologies abstract asteroid 2008 tc3 impacted earth in northern sudan on october 7 2008 the meteorite named almahata sitta was classified as a polymict ureilite in this study 40 small pieces from different fragments collected in the almahata sitta strewn field were investigated and a large number of different lithologies were found some of these fragments are ureilitic in origin whereas others are clearly chondritic as all are relatively fresh w0 w0 1 and as short lived cosmogenic radioisotopes were detected within two of the chondritic fragments there is strong evidence that most if not all belong to the almahata sitta meteorite fall the fragments can roughly be subdivided into achondritic ureilitic 23 samples and chondritic lithologies 17 samples among the ureilitic rocks are at least 10 different lithologies a similar number of different chondritic lithologies also exist most chondritic fragments belong to at least seven different e chondrite rock types eh3 el3 4 el6 el breccias several different types of el and eh impact melt rocks and impact melt breccias some of the latter are shock darkened in addition two h group ordinary chondrite lithologies were identified and one sample of a chondrite type that is so far unique the latter has some affinities to r chondrites oxygen isotope compositions of 14 fragments provide further fundamental information on the lithological heterogeneity of the almahata sitta meteorite based on the findings presented in this study the reflectance spectrum of asteroid 2008 tc3 has to be evaluated in a new light

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

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

ejecta blocks on 243 ida and on other asteroids abstract seventeen positive relief features 45 150 m across are identified as probable blocks in galileo high resolution images of ida their presence provides direct evidence for regolith retention on asteroids the spatial distribution maximum size and integrated volume of the blocks are consistent with those of blocks associated with craters on the earth the moon phobos and deimos the concordance suggests that the features are impact ejecta fragments and that cratering mechanics on ida an object of average diameter 32 km are similar to those applying on previously studied rocky bodies the blocks that lie within or near the rims of craters lascaux and mammoth were likely mobilized in the low velocity tail portion of the excavation flow that formed those craters a few blocks located near smaller craters may have migrated some distance away from their source possibly by impact induced spallation hopping rolling and or sliding some blocks on ida could be surviving fragments from the koronis parent body accreted after its breakup the lifetime of 102 m sized boulders against collisional disruption is estimated to be in the 108 109year range consistent with ages considered for the largest and oldest craters on ida extrapolation of successful ejecta scaling laws to other asteroids suggests that blocks 15 and 70 m across could be present on dactyl and gaspra respectively in both cases too small to be identified in available galileo images blocks 100 m in size could be present on 433 eros and km sized megablocks on 4 vesta

the bholghati howardite petrography and mineral chemistry abstract a 10 g sample of the bholghati howardite was disaggregated in order to separate two eucrite clasts several small carbonaceous clasts fragments of diogenitic pyroxene and bulk matrix the eucrite clasts show evidence of moderately rapid cooling from a melt followed by prolonged subsolidus annealing the carbonaceous clasts mostly resemble cm2 carbonaceous chondrites with low iron silicates and fe ni sulphides in a fine grained dark matrix one clast however is mineralogically petrographically and compositionally similar to a ci 1 chondrite both carbonaceous and eucritic clasts have a complex history prior to incorporation into the howardite matrix with no evidence of significant metamorphism since assembly most clasts in the howardite breccia are monomineralic with pyroxene and plagioclase pre dominant pyroxenes range from diogenitic to eucritic with diogenitic compositions most abundant a significant number of intermediate compositions are present consistent with derivation from a series of rocks related by fractionation

mineralogy of carbonaceous chondrite clasts in hed achondrites and the moon the majority of the carbonaceous chondrite clasts found in howardites eucrites and diogenites are cm2 material a lesser proportion is cr2 material and other rare types are present a single clast that was found on the moon and called the bench crater meteorite is apparently shocked cm1 material the cm2 clasts are matrix supported mixtures of olivine pyroxene phyllosilicate sulfide bearing aggregates loose olivines and pyroxenes sulfides carbonates and sinuous spinel phyllosilicate diopside calcium aluminum rich inclusions cais magnetite and metal are rare some aggregates have fine grained rims of material resembling matrix the opaque fine grained matrix consists predominantly of serpentine of extremely variable composition and sulfides tochilinite is occasionally present the trace element data for one jodzie clast from this study and the average of similar clasts from kapoeta support a cm classification volatiles are depleted relative to ci and enriched relative to cr material the cr2 clasts are found in small numbers in only four howardites bholghati jodzie kapoeta and y793497 petrographically they are matrix supported mixtures of olivine aggregates sometimes containing sulfides loose olivines pyrrhotite pentlandite low ca pyroxene minor hedenbergite rare kamacite rare and only found within olivine ca carbonates and abundant magnetite framboids and plaquets phyllosilicates are fine grained and largely confined to matrix they are mixtures of serpentine and saponite the matrix of cr2 clasts also contains pyrrhotite pentlandite chromite and a significant fraction of poorly crystalline material with the same bulk composition as matrix phyllosilicate there is evidence of heating in a substantial number of clasts both cm2 and cr2 including 1 corrugated serpentine flakes 2 pseudomorphs of anhydrous ferromagnesian material after flaky phyllosilicates and 3 hedenbergite rims on calcite while the timing of the hedenbergite rims is debatable the destruction of phyllosilicates clearly occurred at a late stage plausibly during impact onto the hed asteroid s and moon and required peak heating temperatures on the order of 400 c we note that in general cm2 material was the most common carbonaceous chondrite lithology impacting the hed asteroids with howardites and eucrites taken together as it is for the earth today a total of 61 out of 75 carbonaceous chondrite clasts from hed meteorites belong to the cm clan petrologic grade 2 this is also supported by published siderophile and volatile element data on howardites eucrites and diogenites that are taken to indicate that cm like materials were the most common impactors on the hed asteroid s the ratio of cr cm clasts in hed asteroids is essentially the same as for modern falls at earth this may indicate that the ratio of disaggregated cm2 to cr2 asteroidal material has been approximately constant through the history of the solar system finally our results are also compatible with type 2 carbonaceous chondrites being equivalent to or from the same source as the material that originally accreted to form the hed asteroid

the paris cm chondrite secondary minerals and asteroidal processing abstract we report a petrographic and mineralogical survey of paris a new cm chondrite considered to be the least altered cm identified so far hewins et al 2014 compared to other cms paris exhibits 1 a higher concentration of fe ni metal beads with nickel contents in the range 4 1 8 1 wt 2 the systematic presence of thin lamellae and tiny blebs of pentlandite in pyrrhotite grains and 3 ubiquitous tochilinite cronstedtite associations with higher feo sio2 and s sio2 ratios in addition paris shows the highest concentration of trapped 36ar reported so far for a cm chondrite hewins et al 2014 in combination with the findings of previous studies our data confirm the reliability of 1 the alteration sequence based on the chemical composition of tochilinite cronstedtite associations to quantify the fluid alteration processes and 2 the use of cr content variability in type ii ferroan chondrule olivine as a proxy of thermal metamorphism in contrast the scales based on 1 the fe3 content of serpentine in the matrix to estimate the degree of aqueous alteration and 2 the chemical composition of fe ni metal beads for quantifying the intensity of the thermal metamorphism are not supported by the characteristics of paris it also appears that the amount of trapped 36ar is a sensitive indicator of the secondary alteration modifications experienced by chondrites for both aqueous alteration and thermal metamorphism considering paris our data suggest that this chondrite should be classified as type 2 7 as it suffered limited but significant fluid alteration and only mild thermal metamorphism these results point out that two separated scales should be used to quantify the degree of the respective role of aqueous alteration and thermal metamorphism in establishing the characteristics of cm chondrites

40ar 39ar ages of h chondrite impact melt breccias 40ar 39ar analyses of a total of 26 samples from eight shock darkened impact melt breccias of h chondrite affinity gao guenie lap 02240 lap 03922 lap 031125 lap 031173 lap 031308 nwa 2058 and ourique are reported these appear to record impacts ranging in time from 303 56 ma gao guenie to 4360 120 ma ourique ago three record impacts 300 400 ma ago while two others record impacts 3900 4000 ma ago combining these with other impact ages from h chondrites in the literature it appears that h chondrites record impacts in the first 100 ma of solar system history during the era of the lunar cataclysm and shortly thereafter 3500 4000 ma ago one or more impacts 300 ma ago and perhaps an impact 500 ma ago near the time of the l chondrite parent body disruption records of impacts on the h chondrite parent body are rare or absent between the era of planetary accretion and the lunar cataclysm 4400 4050 ma during the long stretch between heavy bombardment and recent breakup events 3500 1000 ma or at the time of final breakup into meteorite sized bodies 50 ma

on the origin of shocked and unshocked cm clasts in h chondrite regolith breccias cm chondrite clasts that have experienced different degrees of aqueous alteration occur in h chondrite and hed meteorite breccias many clasts are fragments of essentially unshocked cm projectiles that accreted at low relative velocities to the regoliths of these parent bodies a few clasts were heated and dehydrated upon impact these objects most likely accreted at higher relative velocities we examined three clasts and explored alternative scenarios for their formation in the first scenario we assumed that the h and hed parent bodies had diameters of a few hundred kilometers so that their high escape velocities would effectively prevent soft landings of small cm projectiles this would imply that weakly shocked cm clasts formed on asteroidal fragments family members associated with the h and hed parent bodies in the second scenario we assumed that weakly shocked cm clasts were spall products ejected at low velocities from larger cm projectiles when they slammed into the h and hed parent bodies in both cases if most cm clasts turn out to have ancient ages e g 3 4 4 1 ga a plausible source for their progenitors would be outer main belt objects some which may have been dynamically implanted 3 9 ga ago by the events described in the so called nice model on the other hand if most cm clasts have recent ages 200 ma a plausible source location for their parent body would be the inner main belt between 2 1 2 2 au in that case the possible source of the cm clasts progenitors parent fragments would be the breakup 160 ma ago of the parent body 170 km in diameter of the baptistina asteroid family baf

multiple precursors of secondary mineralogical assemblages in cm chondrites we report a petrographic and mineralogical survey of tochilinite cronstedtite intergrowths tcis in paris a new cm chondrite considered to be the least altered cm identified to date our results indicate that type i tcis consist of compact tochilinite cronstedtite rims surrounding fe ni metal beads thus confirming kamacite as the precursor of type i tcis in contrast type ii tcis are characterized by complex compositional zoning composed of three different fe bearing secondary minerals from the outside inwards tochilinite cronstedtite and amakinite type ii tcis present well developed faces that allow a detailed morphological analysis to be performed in order to identify the precursors the results demonstrate that type ii tcis formed by pseudomorphism of the anhydrous silicates olivine and pyroxene hence there is no apparent genetic relationship between type i and type ii tcis in addition the complex chemical zoning observed within type ii tcis suggests that the alteration conditions evolved dramatically over time at least three stages of alteration can be proposed characterized by alteration fluids with varying compositions 1 fe and s rich fluids 2 s poor and fe and si rich fluids and 3 s and si poor fe rich fluids the presence of unaltered silicates in close association with euhedral type ii tcis suggests the existence of microenvironments during the first alteration stages of cm chondrites in addition the absence of mg bearing secondary minerals in paris tcis suggests that the mg content increases during the course of alteration

original structures and fragmentation and reassembly histories of asteroids evidence from meteorites abstract if chondritic meteorites were internally heated after accretion had ended then the hottest material would have been buried the deepest and should have cooled the slowest if this is correct there ought to be a correlation between cooling rate and petrographic type a measure of the extent to which chondrites were metamorphosed i e heated published and new cooling rates derived from the compositions of metallic iron nickel grains do not display this correlation implying either that chondrite parent asteroids never had onion shell structures or that bodies with onion shell structures were broken up and reassembled prior to cooling to below 500 c the temperature at which cooling rate information is recorded in metallic iron nickel chondritic regolith breccias formed from materials that resided on the surfaces of their parent asteroids metallic iron nickel grains in h and l chondrite regolith breccias indicate that the breccia constituents cooled at rates ranging from 1 to 1000 k myr based on thermal calculations these cooling rates suggest that the materials spread out on the surfaces of h and l chondrite parent asteroids originated at depths ranging from about one kilometer to several tens of kilometers craters deep enough to excavate tens of kilometers cannot form on typical asteroidal bodies only 100 to 300 km in diameter without disrupting them therefore it appears that at least some asteroids namely the parent bodies of h and l chondrites were disrupted after cooling to below 300 c and then reassembled to create surfaces containing rocks that originated at a wide range of depths these results support theoretical calculations suggesting that many asteroids were broken up and subsequently reassembled into gravitationally bound rubble piles

fault related folding in sandbox analogue models of thrust wedges abstract the nucleation and growth of thrust fault related folds has been simulated using high resolution sandbox coulomb wedge type analogue models thrust related anticlines grew progressively from initial layerparallel shortening to decollement folding thrust tip folding and eventually thrust ramp folding thrust ramps nucleated in the central sector of the overturned forelimb of decollement folds as a consequence of limb thinning thrust tip folding occurred during outward migration of the ramp tips the fault propagation rate was greater at the lower ramp tip which quickly joined the basal thrust flat while folding continued beyond the upper tip the development of the analogue model thrust fault related folds by progressive changes in kinematics from decollement folding to thrust tip folding and finally thrust ramp folding compares well with analyses of naturally occurring thrust fault related folds

geometric and numerical model of progressive limb rotation in detachment folds a simple area balanced geometric model of progressive limb rotation in detachment folds allows the quantification of displacement uplift and rotation and the assessment of their effect upon growth strata geometries translation of this geometric model into a velocity model of deformation allows the modeling of associated growth strata resulting from background sedimentation and local erosion transport and deposition we show that with constant displacement and sedimentation rate this model predicts a progressive unconformity indicating the onlap and eventual overlap of the fold limb caused by a decreasing uplift rate this decrease is a consequence of the kinematics of progressive limb rotation increases in displacement rate with sedimentation rate kept constant can lead to offlap and angular unconformities although subsequent onlap does not necessarily reflect a return to a lower displacement rate modeled growth strata geometries exhibit many of the features reported from the literature

carbonaceous xenoliths in the krymka ll3 1 chondrite mysteries and established facts abstract the results of a detailed study on mineralogy chemistry and the carbon and oxygen isotopes of two exotic krymka carbonaceous xenoliths are presented in this article the investigated xenoliths are metamorphosed and shocked and have the following characteristics which distinguish them from the krymka host 1 resemblance of their sio 2 mgo ratio to that of carbonaceous chondrites 2 higher fe content and feo feo mgo ratio 3 lower concentration of si ca al and an enrichment of s and probably of ag 4 smaller sizes and lower content 10 vol of chondrules and their clasts and correspondingly higher content of matrix 5 dominance of porphyritic chondrules and lack of nonporphyritic chondrules 6 occurrence of an amoeboid olivine grain with 16 o rich composition 7 existence of carbon in three different forms graphite carbon rich material and organic compounds the bulk chemistry of the xenoliths is similar but not identical to that of carbonaceous chondrites suggesting that they represent a chondrite parent body that has not been previously sampled among any known type of meteoritic material the mineralogy of the xenoliths corresponds only to that of other krymka graphite containing xenoliths it differs however from the latter by having a lower grade of metamorphism we infer that metamorphism of the primary carbonaceous body of the xenoliths and or shock of the krymka parent body are responsible for the major metamorphic alteration of the xenoliths including the crystallization of graphite from primary organic compounds a comparison of the features of the krymka xenoliths with the inferred characteristics of cometary meteorites attests that their genetic relationship to cometary material remains highly inconclusive

fault displacement gradient folds and the structure at lost hills california u s a abstract geometric models of fault propagation folds require that the underlying fault tip propagate upward across layering however related folds can be generated if the tip remains stationary or even moves back along the ramp as a pre existing fault is reactivated fault propagation folds detachment folds as well as those produced when there is no propagation are generated by a displacement gradient along the underlying fault and as a general class can be called fault displacement gradient folds new geometric equations are derived which relate fold shape to displacement gradient and fault propagation folds are a special case of these more general equations growth sequences associated with these structures have been used to distinguish fault propagation folds from fault bend folds when the underlying structure is obscured a displacement gradient fold in which the fault tip retreats back down the ramp generates a growth sequence that in some cases could be confused with that of a fault bend fold the structure at lost hills in the san joaquin valley of california u s a has been interpreted as a fault bend fold but it may be a displacement gradient fold which formed as a pre existing fault was reactivated during a pliocene change in plate motion

self determining numerical modeling of compressional fault bend folding we present the application of the hca hybrid cellular automata numerical modeling technique to the evolution of compressional fault bend anticlines involving layers that have competency contrasts and a mechanical stratigraphy the new modeling results show that for competent hanging wall layers 1 the fault style is not preserved in the overlying fold 2 fold development is not self similar and rotational growth wedges develop in the forelimb when syntectonic sedimentation occurs and 3 balanced fault bend anticlines can develop for ramp cutoff angles as high as 60 these results compare favorably with field examples and laboratory analogues and dramatically broaden the applicability of fault bend folding to model the evolution of thrust related anticlines

mathematical modelling of sedimentary basin processes abstract mathematical models of various sedimentary basin processes including hanging wall deformation evaporite deposition carbonate platform sedimentation and sequence development on active domino style fault blocks are presented many of these processes may be formulated using the equation of continuity of an open system as a starting point sedimentary and tectonic processes may be combined into a single mathematical formulation provided that an eulerian coordinate system is used and this ensures that tectonics and sedimentation are modelled as simultaneous rather than sequential processes the resulting algorithms are fast robust and applicable to many geologically very different situations but may be limited to relatively simple examples the conditions under which the models are numerically stable are also easily found the abstract nature of the mathematical models requires that simply determined properties such as palaeo water depth and palaeo slope must be used as proxy facies markers the main limitation of the method is that it is restricted to modelling processes which change slowly with time and space and the method can therefore not cope properly with episodic or chaotic processes

widespread hydrothermal alteration minerals in the fine grained matrices of the tieschitz unequilibrated ordinary chondrite mineralogic textural and compositional studies of black and white matrices in the unequilibrated ordinary chondrite tieschitz h l 3 6 show for the first time in an ordinary chondrite the presence of widespread randomly distributed geode like voids and veins scanning electron microscope sem and transmission electron microscope tem studies show that these voids and veins are partially or completely filled by sodic calcic amphiboles winchite and barroisite the occurrence of amphiboles provides unequivocal evidence of the involvement of fluids in the metamorphic evolution of the parent body of tieschitz the presence of amphiboles as the main hydrous phases rather than phyllosilicates indicates that aqueous fluids were present at or close to the peak of thermal metamorphism rather than during the waning stages of the cooling history of the parent body in addition ferrous olivine crystals in association with the amphibole also establish an important link between thermal metamorphism and hydrous phases formed at high temperatures mineralogic and textural evidence suggests that the white matrix and amphibole formed contemporaneously from the same hydrous fluid prior to the formation of ferrous olivine crystals additionally a dark inclusion identified in the host chondrite has mineralogic petrologic and bulk chemical characteristics that are similar to the black matrix of host tieschitz suggesting that this dark inclusion was emplaced before or during parent body metamorphism

a strongly hydrated microclast in the rumuruti chondrite nwa 6828 implications for the distribution of hydrous material in the solar system hydrous carbonaceous microclasts are by far the most abundant foreign fragments in stony meteorites and mostly resemble ci1 cm2 or cr2 like material their occurrence is of great importance for understanding the distribution and migration of water bearing volatile rich matter in the solar system this paper reports the first finding of a strongly hydrated microclast in a rumuruti chondrite the r3 6 chondrite northwest africa 6828 contains a 420 325 m sized angular foreign fragment exhibiting sharp boundaries to the surrounding r type matrix the clast is dominantly composed of magnetite pyrrhotite rare ca carbonate and very rare mg rich olivine set in an abundant fine grained phyllosilicate rich matrix phyllosilicates are serpentine and saponite one region of the clast is dominated by forsteritic olivine fa 1 au between the formation regions of ordinary and carbonaceous chondrites the occurrence of a hydrous microclast in an r chondrite attests to the presence of such material also in this region at least at some point in time and documents the wide distribution of water bearing possibly zodiacal cloud material in the solar system

mineralogy and petrography of the almahata sitta ureilite abstract we performed a battery of analyses on 17 samples of the almahata sitta meteorite identifying three main lithologies and several minor ones present as clasts the main lithologies are 1 a pyroxene dominated very porous highly reduced lithology 2 a pyroxene dominated compact lithology and 3 an olivine dominated compact lithology although it seems possible that all three lithologies grade smoothly into each other at the kg scale at the g scale this is not apparent the meteorite is a polymict ureilite with some intriguing features including exceptionally variable porosity and pyroxene composition although augite is locally present in almahata sitta it is a minor phase in most but not all samples we have observed low calcium pyroxene 5 mole wollastonite is more abundant than compositionally defined pigeonite however we found that even the low ca pyroxene in almahata sitta has the monoclinic pigeonite crystal structure and thus is properly termed pigeonite as the major pyroxene in almahata sitta is pigeonite and the abundance of pigeonite is generally greater than that of olivine this meteorite might be called a pigeonite olivine ureilite rather than the conventional olivine pigeonite ureilite group the wide variability of lithologies in almahata sitta reveals a complex history including asteroidal igneous crystallization impact disruption reheating and partial vaporization high temperature reduction and carbon burning and re agglomeration