geochemistry of the ungrouped carbonaceous chondrite tagish lake the anomalous cm chondrite bells and comparison with ci and cm chondrites i have determined the composition via instrumental neutron activation analysis of a bulk pristine sample of the tagish lake carbonaceous chondrite fall along with bulk samples of the ci chondrite orgueil and of several cm chondrites tagish lake has a mean of refractory lithophile element cr ratios like those of cm chondrites and distinctly higher than the ci chondrite mean tagish lake exhibits abundances of the moderately volatile lithophile elements na and k that are slightly higher than those of mean cm chondrites refractory through moderately volatile siderophile element abundances in tagish lake are like those of cm chondrites tagish lake is distinct from cm chondrites in abundances of the most volatile elements mean ci normalized se co zn co and cs co for tagish lake are 0 68 0 01 0 71 0 07 and 0 76 0 02 while for all available cm chondrite determinations these ratios lie between 0 31 and 0 61 between 0 32 and 0 58 and between 0 39 and 0 74 respectively considering petrography and oxygen isotopic and elemental compositions tagish lake is an ungrouped member of the carbonaceous chondrite clan the overall abundance pattern is similar to those of cm chondrites indicating that tagish lake and cms experienced very similar nebular fractionations bells is a cm chondrite with unusual petrologic characteristics bells has a mean ci normalized refractory lithophile element cr ratio of 0 96 lower than for any other cm chondrite but shows ci normalized moderately volatile lithophile element cr ratios within the ranges of other cm chondrites except for na which is low iridium co ni and fe abundances are like those of cm chondrites but the moderately volatile siderophile elements au as and sb have abundances below the ranges for cm chondrites abundances of the moderately volatile elements se and zn of bells are within the cm ranges bells is best classified as an anomalous cm chondrite

origin of fayalitic olivine rims and lath shaped matrix olivine in the cv3 chondrite allende and its dark inclusions we have studied an allende dark inclusion by optical microscopy scanning electron microscopy electron microprobe analysis and transmission electron microscopy the inclusion consists of chondrules isolated olivines and matrix which as in the allende host is mainly composed of 5 20 m long lath shaped fayalitic grains with a narrow compositional range fa42 2 and nepheline olivine phenocrysts in chondrules and isolated olivine grains show various degrees of replacement by 5 10 m wide fayalitic rims fa39 2 and 100 1000 m wide translucent zones which consist of 5 20 m long lath shaped fayalitic grains fa41 1 intergrown with nepheline these fayalitic olivines like those in the matrix of the dark inclusion contain 10 20 nm sized inclusions of chromite hercynite and fe ni sulfides the fayalitic rims around remnant olivines are texturally and compositionally identical to those in allende host suggesting that they have similar origins chondrules are surrounded by opaque rims consisting of tiny lath shaped fayalitic olivines 1 3 m long intergrown with nepheline as in the allende host fayalitic olivine veins may crosscut altered chondrules fine grained chondrule rims and extend into the matrix indicating that alteration occurred after accretion we infer that fayalitic olivine rims and lath shaped fayalites in allende and its dark inclusions formed from phyllosilicate intermediate phases this explanation accounts for 1 the similarity of the replacement textures observed in the dark inclusion and allende host to aqueous alteration textures in cm chondrites 2 the anomalously high abundances of al and cr and the presence of tiny inclusions of spinels and sulfides in fayalitic olivines in allende and allende dark inclusions 3 abundant voids and defects in lath shaped fayalites in the allende dark inclusion which may be analogous to those in partly dehydrated phyllosilicates in metamorphosed cm ci chondrites we conclude that the matrix and chondrule rims in allende were largely converted to phyllosilicates and then completely dehydrated the allende dark inclusions experienced diverse degrees of aqueous hydrothermal alteration prior to complete dehydration the absence of low ca pyroxene in the dark inclusion and its significant replacement by fayalitic olivine in allende is consistent with the lower resistance of low ca pyroxene to aqueous alteration relative to forsteritic olivine hydro thermal processing of allende probably also accounts for the low abundance of planetary noble gases and interstellar grains and the formation of nepheline sodalite salite hedenbergite pyroxenes wollastonite kirschsteinite and andradite in chondrules and ca al rich inclusions

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

refractory inclusions in the prototypical cm chondrite mighei abstract refractory inclusions in the mighei cm2 meteorite are very abundant 35 being found in three thin sections of the meteorite the most common are pyroxene rimmed spinel rich inclusions that occur in a range of structural and textural types some inclusions are simple aggregates of crystals or rimmed crystals ranging from loose clusters of spinel grains to distended chains of pyroxene rimmed spinel knots others are more compact and may have experienced recrystallization or melting these include nodular spinel inclusions with polygonal granular textured spinel interiors and pyroxene rims ribbons of spinel in some cases with hibonite and or perovskite that are again rimmed by pyroxene and refractory spherules four inclusions are complex aggregates of several texturally distinct objects each collectively mighei inclusions are similar to those in murchison but appear to be somewhat more altered volatility fractionated and unfractionated trace element patterns similar to those found in refractory inclusions in other carbonaceous chondrites are represented in mighei inclusions and in addition some mighei inclusions have volatility fractionated pattern types not previously found in refractory inclusions in three of the complex aggregates fundamentally different trace element patterns are present within different portions of each inclusion meaning that these objects accreted from genetically different components that never equilibrated with one another subsequent to accretion bulk inclusion magnesium isotopic compositions show minor mass fractionation effects fmg values range from 2 3 to 7 5 but the average fmg value is indistinguishable from normal 1 8 1 2 there are no correlations between magnesium isotopic composition and textural type or trace element pattern type the diverse inclusion types in mighei represent a variety of origins and histories textures suggest that the nodular and banded inclusions may have experienced solid state recrystallization whereas the porous and chain like varieties and complex aggregates have not magnesium isotopic compositions and trace element abundances suggest that the mighei inclusions are unlikely to be evaporation residues and are more likely to be the products of condensation or recondensation processes

florenskyite fetip a new phosphide from the kaidun meteorite florenskyite is a new phosphide species from the kaidun chondritic meteorite which fell in south yemen in 1980 kaidun is a unique chondritic breccia containing a huge variety of fragments of different chondritic types florenskyite was found as four dispersed grains with a maximum dimension of 14 m within a single mass of fe rich serpentine within one kaidun clast florenskyite is associated with submicrometer sized grains of pentlandite and small up to 1 5 m in width laths of a still uncharacterized fe cr phosphide florenskyite is creamy white in reflected light and its luster is metallic the average of three electron microprobe analyses gave wt fe 40 52 ti 30 08 ni 5 47 cr 0 93 v 0 91 co 0 60 p 21 69 si 0 59 sum 100 79 corresponding to fe1 01 ti0 87ni0 13cr0 03v0 02co0 01 1 06 p0 97si0 03 single crystal structure analysis was performed on florenskyite using a laue pattern collected from a multiple crystal by in situ synchrotron x ray diffraction florenskyite crystallizes in the space group pnma and has the anti pbcl2 structure previously determined cell constants of synthetic material a 6 007 1 b 3 602 1 c 6 897 1 a were used in the single crystal data reduction we used the powd12 program to calculate a powder xrd pattern the 5 most intense reflections are d 2 301 i 100 2 188 88 2 307 47 1 938 45 and 1 801 a 45 florenskyite is only the fourth phosphide to be described from nature its paragenesis may be unique and may be due to melting of a mineral assemblage including fe ni metal schreibersite daubreelite osbornite or heideite and subsequent crystallization of phosphides from the melt

phyllosilicates in the matrix of the unique carbonaceous chondrite lewis cliff 85332 and possible implications for the aqueous alteration of ci chondrites abstract the fine grained matrix of the unique unequilibrated carbonaceous chondrite lewis cliff lew 85332 has been studied by scanning electron microscopy sem electron probe microanalysis epma and transmission electron microscopy tem compositionally lew 85332 has a matrix that is more fe rich than typical ci chondrites but has elemental abundance ratios that appear to be closer to ci matrices than to cm or cr chondrites the mineralogy of the matrix is dominated by phyllosilicate phases that are predominantly interlayered fe rich serpentine saponite anhydrous silicate phases such as olivine and pyroxene are rare minor magnetite troilite and ferrihydrite also occur associated with the phyllosilicates despite the high degree of weathering in lew 85332 the phyllosilicates appear to have an extraterrestrial origin but the highly variable mg fe ratios of saponite may be the result of partial terrestrial oxidation of fe rich saponite to a more mg rich saponite and ferrihydrite alternatively some of the ferrihydrite may have formed as a result of terrestrial weathering of fe ni metal the compositional and mineralogical data suggest that the matrix of lew 85332 may represent a very early stage in the type of aqueous alteration experienced by the ci chondrites although it is improbable that lew 85332 was a precursor to the ci chondrites because of its high abundance of chondrules the absence of carbonates the high fe content of the matrix and phyllosilicate phases and relatively low abundance of magnetite all indicate that the degree of oxidation and leaching of lew 85332 matrix was significantly less than that experienced by the ci chondrites the absence of clear evidence for alteration of chondrules suggests that either the formation of the hydrous phases in the matrix occurred prior to accretion or that alteration occurred on a parent body and involved limited amounts of fluid such that the reactions took place preferentially and exclusively within the fine grained anhydrous matrix materials

incompletely transformed serpentine type phyllosilicates in the matrix of antarctic cm chondrites abstract recent hrem high resolution electron microscopy investigation has shed light on the characterization of matrix phyllosilicates in cm chondrites in examining the antarctic cm chondrite yamato 793321 by hrem mineral grains which show an ed electron diffraction pattern consisting of both olivine and serpentine spots show disordered and defect structures in patchy hrem images these data are interpreted as representing an intermediate phase in the transformation from serpentine to olivine this is the first description of such an intermediate phase in belgica 7904 phyllosilicates seem to have been almost completely transformed to olivine it is suggested that it formed by heating of matrix phyllosilicates preliminary heating experiments on murchison also a cm chondrite showed that the matrix phyllosilicates transformed to a phase which gave an ed pattern and hrem image similar to those for yamato 793321 the results of these heating experiments support the formation of the intermediate phase by transformation from phyllosilicate to olivine during a heating event at a late stage

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

the fall recovery orbit and composition of the tagish lake meteorite a new type of carbonaceous chondrite the preatmospheric mass of the tagish lake meteoroid was about 200 000 kilograms its calculated orbit indicates affinity to the apollo asteroids with a semimajor axis in the middle of the asteroid belt consistent with a linkage to low albedo c d and p type asteroids the mineralogy oxygen isotope and bulk chemical composition of recovered samples of the tagish lake meteorite are intermediate between cm and ci meteorites these data suggest that the tagish lake meteorite may be one of the most primitive solar system materials yet studied

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

structural trends in the northern red sea the northern red sea is underlain by a series of plio pleistocene sedimentary sequences that unconformably overlie evaporitic series of late miocene age a series of bathyal rifts and cogenetic diapirs trending approximately n s were recently discovered in that region between latitude 26 30 n and 28 n the rifts are up to 60 km long and 7 km wide and the diapirs commonly ascended along the rifts boundary faults the diapirs stem from the late miocene evaporites thus the discerned structural trends were developed during the plio pleistocene the encountered structural patterns deviate considerably from the nw se structural trends that prevail in the central red sea as well as in the faults that border the northern red sea and the gulf of suez the tectonic activity that formed the suez rift in the middle to late miocene was not rejuvenated there during the plio pleistocene and the new data indicate that the axis of the tectonic extension at the northern red sea jumped to show a northward orientation it is suggested that incipient spreading center extends from the red sea northward to the gulf of elat and the dead sea rift

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

accretionary dust mantles in cm chondrites evidence for solar nebula processes abstract the texture and modal composition of fourteen carbonaceous chondrites of the cm group were studied in detail to unravel the origin of their various components and the evolution of their parent body ies the analysis and mapping of complete thin sections by scanning electron and optical microscopy revealed textural units in most samples in which all coarse grained primordial chondritic components chondrules chondrule fragments refractory inclusions particles rich in hydrous silicates pcp and various mineral fragments are coated by fine grained serpentine and tochilinite rich dust the dust mantled particles have spheroidal shapes and form a special lithology in which they are densely aggregated and compacted without any interstitial clastic material the dust mantles termed accretionary dust mantles and their host lithology called primary accretionary rock are interpreted as products of accretion processes in the solar nebula an origin by processes on the parent body is excluded for textural and mineralogical reasons most cm chondrites are affected by secondary impact induced brecciation of variable intensity except for yamato 791198 which is composed entirely of a primary accretionary rock obviously unaltered by secondary parent body processes such as aqueous alteration or brecciation the cm chondrites y74662 haripura cold bokkeveld kivesvaara mighei pollen nogoya y793321 alh 83100 murray and murchison consist of clasts of primary accretionary rock embedded in a fine grained clastic matrix derived from primary rock material the volume percentage of the clastic matrix ranges from 5 y74662 to 76 murchison bells and essebi are brecciated and affected by aqueous alteration to an extent that fragments of primary rock are not preserved the evaluation of literature data indicates that solar wind implanted noble gases are absent in the primary accretionary rock component of cm chondrites they are only present in brecciated samples it must be concluded from the relation between the content of trapped solar wind and degree of brecciation that 1 the solar noble gases are residing exclusively in the clastic matrix and 2 some cm chondrites are regolith breccias and others are fragmental or monomict breccias both types were formed on the parent body although the latter were never exposed to the solar wind based on the results of textural chemical and mineralogical investigations we conclude that a major portion of the water bearing phases in cm chondrites were produced by the hydration of refractory phases prior to the formation of dust mantles and prior to the formation of the recent cm parent body this process requires special physicochemical conditions which allow the crystallization of oh bearing silicates e g higher density of the nebula gas or special precursor planetesimals of the cm chondrite parent body

formation and alteration of cais in cold bokkeveld cm2 abstract calcium aluminium rich inclusions cais from the carbonaceous chondrite cold bokkeveld cm2 have been located and characterised in situ the textural environment of cm2 cais has been studied for the first time based on their primary mineralogy 345 cais have been classified into four groups 1 1 spinel inclusions 2 2 a hibonite inclusion 3 3 spinel pyroxene sp py inclusions 4 4 spinel pyroxene olivine sp py ol inclusions in addition refractory spherules and spinel bearing isolated olivines are also recognised cais in cold bokkeveld underwent extensive aqueous alteration and contain secondary minerals including calcite and various phyllosilicates these assemblages are similar to those in the chondrules and matrix of the meteorite and it is concluded that all were altered more or less simultaneously within a parent body regolith as is common in cm2s most cais in cold bokkeveld have a rim sequence containing a prominent fe rich phyllosilicate layer this formed early in the alteration sequence by the dissolution of melilite and subsequent precipitation of fe rich phyllosilicates from fluids with a high fe mg ratio cais in cold bokkeveld experienced two stages of deformation an earlier nebula stage predated the formation of the dust mantles that surround most cais and a later stage occurred in an asteroidal regolith the cais in cm2s are smaller than those in cv3 chondrites because of the greater intensity of the earlier fragmentation episode that they experienced aqueous alteration of cais and regolith deformation appear to have been simultaneous phase relations and pyroxene compositional trends in sp py and sp py ol inclusions indicate that they crystallised from liquids most spinel bearing inclusions in cold bokkeveld have a normal mg isotopic composition so they could not have formed by the simultaneous melting and evaporation of primitive dust one inclusion is enriched in the heavy isotopes of mg and may have formed in this way two or more events are required to form most of the inclusions the first produced the refractory compositions either by vapour solid condensation or slow evaporation of primitive dust the second event melted the refractory precursors which later crystallised to form the observed textures and mineral assemblages it has been suggested that refractory spherules with inwardly radiating hibonites formed from molten droplets at temperatures as high as 2135 c however the crystallisation sequences of these inclusions inferred from textural evidence are incompatible with those derived from phase relations and estimates of bulk composition it is concluded that cm2 refractory spherules did not form by crystallisation of molten droplets but were derived by fragmentation of larger inclusions in which they formed by partial melting

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

diradicaloids in the insoluble organic matter from the tagish lake meteorite comparison with the orgueil and murchison meteorites the radicals in the insoluble organic matter iom from the tagish lake meteorite were studied by electron paramagnetic resonance and compared to those existing in the orgueil and murchison meteorites as in the orgueil and murchison meteorites the radicals in the tagish lake meteorite are heterogeneously distributed and comprise a substantial amount 42 of species with a thermally accessible triplet state and with the same singlet triplet gap e 0 1 ev as in the orgueil and murchison meteorites these species were identified as diradicaloid moieties the existence of similar diradicaloid moieties in three different carbonaceous chondrites but not in terrestrial iom strongly suggests that these moieties could be fingerprints of the extraterrestrial origin of meteoritic iom and markers of its synthetic pathway before its inclusion into a parent body

the kaidun meteorite mineralogy of an unusual cm1 lithology kaidun is a breccia of disparate enstatite and carbonaceous chondrite clasts that continues to provide real surprises many kaidun clasts have been intensely altered by aqueous fluids as evidenced by the widespread occurrence of ferromagnesian phyllosilicates and by the presence of carbonate and phyllo silicate filled veins in this report we describe an unusual cm lithology containing many mineralogical features not previously reported from any meteorite including pyrrhotite with exclusive needlelike morphologies and thick mantles of phyllosilicate and complex aggregates of phyllosilicate melanite garnet crosscut by pentlandite veins the latter features appear to be due in large part to extensive hydrothermal alteration at temperatures on the order of 450 c which is significantly higher than that attained during secondary processing from other known cm material

the porosity and permeability of chondritic meteorites and interplanetary dust particles abstract we have investigated the porosity of a large number of chondritic interplanetary dust particles idps and meteorites by three techniques standard liquid gas flow techniques a new noninvasive ultrasonic technique and image processing of backscattered images the latter technique is obviously best suited to sub kilogram sized samples we have also measured the gas and liquid permeabilities of some chondrites by two techniques standard liquid gas flow techniques and a new nondestructive pressure release technique we find that chondritic idps have a somewhat bimodal porosity distribution peaks are present at 0 and 4 porosity a tail then extends to 53 type 1 3 chondrite matrix porosities range up to 30 with a peak at 2 the bulk porosities for type 1 3 chondrites have the same approximate range as exhibited by the matrix which indicates that other components of the bulk meteorites including chondrules and aggregates have the same average porosity as the matrix these results reveal that the porosities of primitive materials at scales ranging from nanogram to kilogram are similar which implies that similar accretion dynamics operated through 12 orders of size magnitude permeabilities of the investigated chondrites vary by several orders of magnitude and there appears to be no simple dependence of permeability with degree of aqueous alteration chondrite type or porosity

the density and porosity of meteorites from the vatican collection abstract we have developed a nondestructive technique to measure the densities and porosities of large 50 g to several kilogram meteorite samples and have begun a systematic measurement program starting with meteorites from the vatican observatory collection our technique utilizes a modified archimedean method 40 m glass spheres substituting for the fluid to determine bulk density and an unusually large he pycnometer to determine grain density from these the porosity is calculated we report here our first results for 89 samples nearly doubling the published database on porosities of meteorite hand samples including porosities of 35 different meteorites these include several types not previously reported eight iron meteorites six stony iron meteorites an enstatite chondrite the ci carbonaceous chondrite orgueil and the shergottite nakhlatite chassignite snc meteorite nakhla

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

extended chronologies of aqueous alteration in the cm2 carbonaceous chondrites evidence from carbonates in queen alexandra range 93005 abstract the antarctic cm2 carbonaceous chondrite que 93005 contains four compositionally distinct carbonates namely breunnerite calcite dolomite and a ca poor dolomite these carbonates can form monomineralic grains or may be intergrown as bimineralic grains consisting of dolomite plus breunnerite and dolomite plus calcite or polymineralic grains containing an intergrowth of breunnerite ca poor dolomite and calcite carbonates in all grain types have inclusions of fe ni sulphides and or mg fe phyllosilicates in the bimineralic grains dolomite crystallised first to be overgrown by breunnerite or partially replaced by calcite polymineralic grains are concentrically layered with breunnerite crystallising first on pore margins to be later etched then overgrown and partially replaced by ca poor dolomite that was itself partly dissolved prior to being overgrown by calcite calcite and dolomite have also cemented fractures that cross cut the fine grained rims to aqueously altered chondrules and were formed by expansion of the chondrules during their hydration overall the sequence of mineralisation in que 93005 was 1 dolomite 2 breunnerite 3 ca poor dolomite then 4 calcite this secular change in carbonate composition and mineralogy reflects changing solution composition and probably also provenance mg fe phyllosilicates replaced dolomite breunnerite and ca poor dolomite prior to calcite crystallisation and most or all of the sulphides formed after both the phyllosilicates and calcite following sulphide crystallisation the edges of carbonate grains were abraded either by impact gardening or as a consequence of fluidisation of the matrix during rapid loss of gas or vapour determination of the crystallisation age of dolomite via the mn cr system indicates that aqueous alteration of que 93005 began on or before 3 93 0 23 ma after the formation of the oldest solar system solids overall the water rock ratio and fo2 during alteration of que 93005 was similar to that of the cm1s and cr1s but the lower degree of alteration of que 93005 overall suggests that alteration timescales were shorter possibly due to loss of intergranular liquid water during fluidisation

comparison of the trace element composition of tagish lake with other primitive carbonaceous chondrites a meteorite fall on 18 january 2000 was detected by u s defense department satellites which established its pre impact orbit fresh samples were collected from frozen tagish lake in british columbia a week later and some properties of these samples reveal it to be a unique meteorite we characterized tagish lake and 8 other samples using icpms and rnaa data for 47 elements reveal that each of 9 carbonaceous chondrites of different type exhibit the orgueil normalized plateaus expected for members of such types trends evident in tagish lake differ from all other carbonaceous chondrites including ci and cm samples of tagish lake collected later show similar patterns affected by weathering

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

deuterium enrichments in chondritic macromolecular material implications for the origin and evolution of organics water and asteroids here we report the elemental and isotopic compositions of the insoluble organic material iom isolated from several previously unanalyzed meteorites as well as the reanalyses of h isotopic compositions of some previously measured samples alexander et al 2007 the iom in ordinary chondrites ocs has very large d enrichments that increase with increasing metamorphism and decreasing h c the most extreme d value measured being almost 12 000 we propose that such large isotopic fractionations could be produced in the oc parent bodies through the loss of isotopically very light h2 generated when fe was oxidized by water at low temperatures 200 c we suggest that similar isotopic fractionations were not generated in the iom of cv and co chondrites with similar metamorphic grades and iom h c ratios because proportionately less water was consumed during metamorphism and the remaining water buffered the h isotopic composition of the iom even a h was being lost from it hydrogen would also have been generated during the alteration of ci cm and cr carbonaceous chondrites the iom in these meteorites exhibit a considerable range in isotopic compositions but all are enriched in d as well as 15n relative to terrestrial values we explore whether these enrichments could also have been produced by the loss of h2 but conclude that the most isotopically anomalous iom compositions in meteorites from these groups are probably closest to their primordial values the less isotopically anomalous iom has probably been modified by parent body processes the response of iom to these processes was complex and varied presumably reflecting differences in conditions within and between parent bodies the d enrichments associated with h2 generation along with exchange between d rich iom and water in the parent bodies means that it is unlikely that any chondrites retain the primordial h isotopic composition of the water ice that they accreted the h isotopic compositions of the most water rich chondrites the cms and cis are probably the least modified and their compositions d 25 suggest that their water did not form at large radial distances from the sun where ice is predicted to be very d rich yet models to explain the o isotopic composition of inner solar system bodies require that large amounts of ice were transported from the outer to the inner solar system

replacement of olivine by serpentine in the queen alexandra range 93005 carbonaceous chondrite cm2 reactant product compositional relations and isovolumetric constraints on reaction stoichiometry and elemental mobility during aqueous alteration abstract isovolumetric replacement of euhedral and anhedral olivine by serpentine produced both centripetal and meshwork textures in the cm2 chondrites alh 81002 and nogoya the compositions of these textural varieties of serpentine are uniform within narrow limits within each previously studied meteorite independent of the composition of olivine being replaced and different between the two meteorites in que 93005 cm2 coarse olivines of widely varying compositions fo are replaced in a texturally similar manner by compositionally uniform serpentine mg 0 73 0 05 fe 0 27 0 05 3 si 2 o 5 oh 4 the narrow compositional range of serpentine replacing coarse olivine indicates that the aqueous solution from which the serpentine formed was compositionally uniform on scales at least as large as the meteorite 2 5 cm in longest dimension isovolumetric textures and compositional observations constrain elemental redistribution from coarse olivine to serpentine and to surrounding phases during serpentinization regardless of olivine s composition isovolumetric replacement of coarse olivines by serpentine of the observed composition released more mg and si from olivine than was required to form the serpentine excess mg and si released by olivine destruction and not retained in serpentine were exported from the replaced volume olivines with different fa fo proportions contributed different amounts of fe and mg to the serpentine ferroan olivines released more fe than required to form the serpentines replacing them so some of the fe released from ferroan olivine was exported from the replaced volumes forsteritic olivines released less fe than required to form the serpentines replacing them so some fe was imported into the replaced volumes augmenting the small amount of fe released from forsteritic olivine in que 93005 fo 83 8 is the threshold composition between fe exporting and fe importing behavior in individual olivine serpentine pairs which released exactly the amount of fe required to form serpentine of the observed uniform composition compositions of serpentines isovolumetrically replacing olivines and threshold olivine compositions in que 93005 differ from the corresponding values in nogoya solvent and solute species diffused through the serpentine between the olivine serpentine interface and the aqueous solution outside the isovolumetrically replaced volume in que 93005 some of the fe released from ferroan olivine in excess of the amount required to form serpentine reacted with s sourced from outside the pseudomorphs to form fe sulfide decorating the margins of the pseudomorphs of serpentine after fayalitic olivine such fe sulfide decorated outlines after fayalitic olivine do not occur in alh 81002 or nogoya indicating different fe and s mass transfer regimes in different cm2 chondrites mg fe si and s in the aqueous solution including the excess mg and si exported from all serpentine pseudomorphs after olivine of any composition were available to be incorporated into other phases spatially separate from the pseudomorphs after olivine including regularly interstratified serpentine tochilinite serpentines that replaced coarse olivines in que 93005 and alh 81002 are less magnesian than those in nogoya indicating that the nogoya aqueous alteration environment was more evolved toward mg rich solutions this easily located and characterized phase assemblage may be potentially useful for characterizing clasts of varying degrees of alteration in brecciated and heterogeneous cm chondrites and future returned samples from mineralogically similar asteroids

correlated alteration effects in cm carbonaceous chondrites three parameters are proposed to determine the relative extent of alteration in cm chondrites the mineralogic alteration index monitors the relative progress of coupled substitutions in the progressive alteration of cronstedtite to mg serpentine and increases with increasing alteration to calculate values of this index an algorithm has been developed to estimate the average matrix phyllosilicate composition in individual cm chondrites the second parameter is the volume percent of isolated matrix silicates which decreases with progressive alteration due to mineral hydration finally the volume percent of chondrule alteration monitors the extent of chondrule phyllosilicate production and increases as alteration proceeds these parameters define the first cm alteration scale that relies on multiple indicators of progressive alteration the following relative order of increasing alteration is established by this model murchison bells pollen murray mighei nogoya cold bokkeveld the relative degree of aqueous processing cochabamba and boriskino experienced is less precisely constrained although both fall near the middle of this sequence a comparison between the mineralogic alteration index and literature values for the whole rock chemistry of cm chondrites reveals several correlations a positive nearly linear correlation between bulk h content and progressive cm alteration suggests an approximately constant production rate of new phyllosilicates relative to the mineralogical transition from cronstedtite to mg serpentine the abundance of trapped planetary 36ar decreases systematically in progressively altered cm chondrites suggesting the wholesale destruction of primary noble gas carrier phase s by aqueous reactions because low temperature fluid rock reactions are generally associated with large isotopic mass fractionation factors we also compared our model predictions with 18o values for bulk cm samples although some of these data are poorly resolved the order of increasing 18o values approximates the order of increasing alteration predicted by our model parameters multiple correlations between diverse alteration parameters strongly suggest that a different cm chondrites experienced similar kinds of processes and conditions and b cm materials experienced in situ alteration on the cm parent body or bodies

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

cm chondrites exhibit the complete petrologic range from type 2 to 1 we have characterized the most phyllosilicate rich members of the cm chondrite group based upon petrographic and compositional factors we conclude that these particular meteorites have experienced pervasive aqueous alteration far beyond that witnessed by typical cms the lack of anhydrous silicates cai and except as relicts chondrules merits the classification of type cmi for three meteorites eet 83334 alh 88045 and one kaidun lithology still other cms notably alh 83100 eet 90047 and yamato 82042 are clearly intermediate between types 1 and 2 brecciated cm chondrites like cold bokkeveld contain all of these varied lithologies the cm chondrites thus exhibit the complete petrologic range from 2 through 1 our results show that progressive aqueous alteration on the parent cm asteroid s was locally accompanied by significant increases in temperature to a peak of 450 c for the kaidun lithology fo2 and locally degree of chemical leaching all well beyond the conditions recorded by typical cm2s the most altered cms also are commonly deformed displaying a distinct lineation probably due to static rather than dynamic forces

variability absorption features and parent body searches in spectrally featureless meteorite reflectance spectra case study tagish lake abstract reflectance spectra of many asteroids and other solar system bodies are commonly reported as featureless here we show that weak but consistently detectable absorption bands are observable in 200 2500 nm spectra of the tagish lake meteorite a likely compositional and spectral analogue for low albedo spectrally featureless asteroids tagish lake presents a rare opportunity to study multiple lithologies within a single meteorite reflectance spectra of tagish lake display significant variation between different lithologies the spectral variations are due in part to mineralogical variations between different tagish lake lithologies ultraviolet reflectance spectra 200 400 nm few of which have been reported in the literature to date reveal albedo and spectral ratio variations as a function of mineralogy similarly visible near infrared reflectance spectra reveal variations in albedo spectral slope and the presence of weak absorption features that persist across different lithologies and can be attributed to various phases present in tagish lake these observations demonstrate that significant spectral variability may exist between different lithologies of tagish lake which may affect the interpretation of potential source body spectra it is also important to consider the spectral variability within the meteorite before excluding compositional links between possible parent bodies in the main belt and tagish lake tagish lake materials may also be spectral compositional analogues for materials on the surfaces of other dark asteroids including some that are targets of upcoming spacecraft missions tagish lake has been proposed as a spectral match for ultra primitive d or p type asteroids and the variability reported here may be reflected in spatially or rotationally resolved spectra of possible tagish lake parent bodies and source objects in the near earth asteroid population a search for objects with spectra similar to tagish lake has been carried out among the near earth asteroids we have identified three possible spectral matches the best of which are asteroids 326732 2003 hb6 and 17274 2000 lc16

shock metamorphism of carbonaceous chondrites abstract we have studied shock effects in carbonaceous chondrites using optical microscopy of thin sections and find that our petrographic classification of progressive shock metamorphism in ordinary chondrites can also be applied to carbonaceous chondrites we find that sixty nine carbonaceous chondrites can be assigned to four shock stages si to s4 largely on the basis of shock effects in olivine the least shocked chondrite groups are cm2 and co3 thirty six out of thirty eight members are classified as shock stage s1 differences between the mean shock levels of certain groups of chondrites e g co3 and cv3 are probably due to stochastic differences in the sampling of their parent bodies however there is an overall tendency for the mean shock level of carbonaceous chondrites and ordinary chondrites to increase with increasing petrologic type that may reflect real differences in the shock level of near surface materials on their parent bodies caused by intrinsic variations in the chemical and physical properties of these materials petrologic type 2 and 3 chondrites are more porous and richer in volatiles than types 4 to 6 the greater porosity of types 2 3 causes higher post shock temperatures and melting at lower pressures and the higher volatile contents ensure that strongly shocked material is more readily dispersed on release from high pressure we suggest that type 2 3 material shocked above 20 30 gpa normally escapes from the parent asteroids and forms particles that are too small to survive as meteorites in the cv3 group there is a correlation between the degree of chondrule flattening and the intensity of shock metamorphism analogous to that discovered in ordinary chondrites by sneyd et al 1988 suggesting that shock rather than static overburden pressure is responsible for chondrule flattening we infer that the correlations are due to collapse of pores under shock pressures of at least 5 10 gpa and that shock is an important process affecting many physical properties of type 2 4 chondrites

accretional and alterational differences in a carbonaceous chondrite parent body evidence from the nwa 5491 cv3 meteorite the nwa 5491 cv3 meteorite is a cvoxa subtype and composed of two substantially different units titled upper and lower units in the cm size range with original accreted material and also subsequent alteration produced features based on the large chondrules in the upper unit and the small chondrules plus cais in the lower unit they possibly accreted material from different parts of the solar nebula and or at different times whereas substantial changes happened in the nebula s composition differences are observed in the level of early fragmentation too which was stronger in the upper units during later alteration oxidizing fluids possibly circulated only in the upper unit mechanical fragmentation and resorption were also stronger there in the last phase of the geological history these two rock units came into physical contact but impact driven shock effects were not observed the characteristics of this meteorite provide evidence that the same parent body might accrete substantially different material and also the later processes could differ spatially in the parent body

origin of the pluto charon system constraints from the new horizons flyby abstract new horizon s accurate determination of the sizes and densities of pluto and charon now permit precise internal models of both bodies to be constructed assuming differentiated rock ice structures we find that pluto is close to 2 3 solar composition anhydrous rock by mass and charon 3 5 solar composition anhydrous rock by mass pluto and charon are closer to each other in density than to other large 1000 km diameter kuiper belt bodies despite this we show that neither the possible presence of an ocean under pluto s water ice shell and no ocean within charon nor enhanced porosity at depth in charon s icy crust compared with that of pluto are sufficient to make pluto and charon s rock mass fractions match all four small satellites styx nix kerberos hydra appear much icier in comparison with either pluto or charon in terms of a giant impact origin both these inferences are most consistent with the relatively slow collision of partly differentiated precursor bodies canup astrophys j 141 35 2011 this is in turn consistent with dynamical conditions in the ancestral kuiper belt but implies that the impact precursors themselves accreted relatively late and slowly to limit 26 al and accretional heating the iciness of the small satellites is not consistent with direct formation of the pluto charon system from a streaming instability in the solar nebula followed by prompt collapse of gravitationally bound pebble piles a proposed formation mechanism for kuiper belt binaries nesvorn et al astron j 140 785 793 2010 growth of pluto scale bodies by accretion of pebbles in the ancestral kuiper belt is not ruled out however and may be needed to prevent the precursor bodies from fully differentiating due to buried accretional heat prior to the charon forming impact

a terrestrial origin for sulfate veins in ci1 chondrites white sulfate veins are a very well known petrological feature of the chemically primitive ci1 carbonaceous chondrites sulfate veins were first described in the orgueil meteorite in 1961 almost one century after its fall however we have observed such veins to form easily during typical sample storage we suggest that all ci1 sulfate veins formed during the terrestrial residence of these heavily brecciated porous stones reacting with atmospheric water sulfates originally present in the meteorites dissolved and remobilized and or sulfides oxidised filling the many open spaces offered to them by the very porous rock sulfate veins in ci1 chondrites can no longer be used as evidence of a late stage oxidation event in the ci1 parent body or of centimeter scale fluid transport on the parent asteroid

on the nature of the link between the lake baikal biogenic silica record and regional climate change in siberia a reply to m a grachev

northwest africa 5958 a weakly altered cm related ungrouped chondrite not a ci3 northwest africa nwa 5958 is a carbonaceous chondrite found in morocco in 2009 preliminary chemical and isotopic data leading to its initial classification as c3 0 ungrouped have prompted us to conduct a multitechnique study of this meteorite and present a general description here the petrography and chemistry of nwa 5958 is most similar to a cm chondrite with a low degree of aqueous alteration apparently under oxidizing conditions and evidence of a second limited alteration episode manifested by alteration fronts the oxygen isotopic composition with delta o 17 4 3 parts per thousand is more o 16 rich than all cm chondrites indicating along with other compositional arguments a separate parent body of origin we suggest that nwa 5958 be reclassified as an ungrouped carbonaceous chondrite related to the cm group

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