a new calcium aluminate from a refractory inclusion in the leoville carbonaceous chondrite abstract the first meteoritic occurrence of caal4o7 is described from a ca al rich inclusion cai in the leoville carbonaceous chondrite this cai consists mainly of gehlenitic melilite spinel perovskite and hibonite caal4o7 is a minor component and occurs within melilite preferentially in portions rich in perovskite the cai is enveloped by a succession of three rims from inside out a hibonite melilite spinel perovskite b diopside and c olivine on the basis of mineral associations found and from the presence of moderately volatile elements fe and cr we conclude that the caal4o7 bearing cai from leoville is of residual nature caal4o7 is apparently stable in the very mg and si poor environment of this cai and is probably of igneous origin the rims are interpreted as products of partial evaporation rim a and associated re condensation rims b and c

hydrogen sulphide and methane emissions on the central namibian shelf abstract hydrogen sulphide occurs frequently in the waters of the inner shelf coastal upwelling area off central namibia the area affected coincides with hatching grounds of commercially important pelagic fish whose recruitment may be severely affected by recurring toxic sulphidic episodes both episodic biogenic methane gas driven advective and molecular diffusive flux of hydrogen sulphide have been implicated as transport mechanisms from the underlying organic matter rich diatomaceous mud to test hypotheses on the controls of hydrogen sulphide transport from the sediments on the inner namibian shelf water column and sediment data were acquired from four stations between 27 and 72 m water depth over a 3 year long period on 14 cruises temperature salinity dissolved oxygen nitrate methane and total dissolved sulphide were determined from water column samples and pore water dissolved methane total dissolved sulphide biomass of benthic sulphide oxidising bacteria beggiatoa and thiomargarita and bacterial sulphate reduction rates were determined from sediment cores superimposed on a trend of synchronous changes in water column oxygen and nutrient concentrations controlled by regional hydrographic conditions were asynchronous small scale variations at the in shore stations that attest to localized controls on water column chemistry small temporal variations in sulphate reduction rates determined with 35 s labeled sulphate do not support the interpretation that variable emissions of sulphide and methane from sediments are driven by temporal changes in the degradation rates of freshly deposited organic matter the large temporal changes in the concentrations of hydrogen sulphide and the co occurrence of pore water sulphate and methane support an interpretation of episodic advection of methane and hydrogen sulphide from deeper sediment depths possibly due to gas bubble transport effective fluxes of hydrogen sulphide and methane to the water column and methane and sulphide concentrations in the bottom waters were decoupled likely due to the activity of sulphide oxidising bacteria while the causal mechanism for the episodic fluctuations in methane and dissolved sulphide concentrations remains unclear this data set points to the importance of alternating advective and diffusive transport of methane and hydrogen sulphide to the water column

mineralogy and petrology of chondrules and inclusions in the mokoia cv3 chondrite all objects 100 m in apparent diameter in five polished thin sections of the mokoia cv3 chondrite were studied and classified number and volume percentages and mean apparent size of each type of chondrule and inclusion were determined three major types of olivine chondrules were observed igneous chondrules recrystallized chondrules and chondrules that appear to be accretional aggregates coarse grained cai s have igneous textures and mineral parageneses while fine grained cai s are aggregates containing varying proportions of al rich concentric objects ca rich chaotic material and inclusion matrix chondrules and refractory inclusions in mokoia and allende are broadly similar in texture and mineral chemistry but mokoia refractory inclusions contain phyllosilicates rather than feldspathoids and melilite rich cai s are more abundant in allende we think that most cai s formed during the metamorphism partial melting and incomplete distillation of primitive dust aggregates when they were heated in the solar nebula in the process ca rich melt appears to have been physically separated from al rich residues producing the observed fractionation of ca from al into distinct constituents of cai s some cai s may be aggregates of devitrified amorphous metastable condensates inclusion matrix may have condensed from silicate rich vapors produced during distillation mokoia inclusion matrix contains phyllosilicates that are probably primitive nebular material

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

mineralogy of chondritic interplanetary dust particles from a mineralogical survey of approximately 30 chondritic micrometeorites collected from the lower stratosphere and studied in detail using current electron microscopy techniques it is concluded that these particles represent a unique group of extraterrestrial materials these micrometeorites differ significantly in form and texture from components of carbonaceous chondrites and contain some mineral assemblages which do not occur in any meteorite class electron microscope investigations of chondritic micrometeorites have established that these materials 1 are extraterrestrial in origin 2 existed in space as small objects 3 endured minimal alteration by planetary processes since formation and 4 can suffer minimal pulse heating 600 c on entering earth s atmosphere the probable sources for chondritic interplanetary dust particles idps are cometary and asteroidal debris and perhaps to a lesser extent interstellar regions these sources have not been conclusively linked to any specific mineralogical subset of idp although the chondritic porous cp aggregate is considered of likely cometary origin chondritic idps occur in two predominant mineral assemblages 1 carbonaceous phases and phyllosilicates and 2 carbonaceous phases and nesosilicates or inosilicates although particles with both types of silicate assemblages are observed olivines pyroxenes layer silicates and carbon rich phases are the most commonly occurring minerals in many chondritic idps other phases often observed in variable proportions include sulphides spinels metals metal carbides carbonates and minor amounts of sulphates and phosphates individual mineral grain sizes range from micrometers primarily pyroxenes and olivines to nanometers with the predominant size for all phases less than 100 nm specific mineral characteristics for particular chondritic idps provide an indication of processes which may have occurred prior to collection in the earth s stratosphere for example pyroxene mineralogy in some chondritic aggregates is consistent with condensation from a vapor phase and we consider with condensation in a turbulent solar nebula at relatively low temperatures 1000 c carbonaceous phases present in other cp aggregates have been used to imply low temperature formation processes such as fischer tropsch synthesis 530 c or carbonization and graphitization 315 c alteration processes have been implicated in the formation of some layer silicates in cp aggregates and may have involved hydrocryogenic alteration at 0 c in general interpretations of transformation processes on submicrometer size minerals in chondritic idps are consistent with formation at a radius equivalent to the asteroid belt or greater during the later stages of solar nebula evolution using currently available models

size distributions in two porous chondritic micrometeorites quantitative size measurements of granular units gus and nanometer sized minerals in these units in two porous chondritic micrometeorites are investigated for the information that they carry on the processes in the early solar system the matrix of these micrometeorites consist of loosely packed 0 1 m sized gus these objects were a major component of the solar nebula dust that accreted into protoplanets the matrix in micrometeorite w7010 a2 has a fractal dimension with a small coefficient d 0 83 that supports efficient sticking of carbon rich gus during accretion the fractal nature of the matrix provides a way to calculate the density using the aggregate size the resulting very low density for porous chondritic micrometeorites is 0 08 0 14 g cm 3 which supports the view that they are the solid debris from unconsolidated solar system bodies e g comet nuclei or regolith deposits on carbon rich asteroids chondritic gus contain ultrafine olivines pyroxenes and sulfides embedded in hydrocarbons and amorphous carbons nanocrystals in the micrometeorites w7010 a2 and u2015 b show log normal size distributions the high incidence of disk shaped grains a changeover from disk shaped to euhedral grains the unevolved nature of the size distributions and multiple populations for grains 127 nm in size are consistent with continuous post accretion nucleation and growth in amorphous gus including coarsening via ostwald ripening

dark inclusions in allende leoville and vigarano evidence for nebular oxidation of cv3 constituents dark lithic inclusions are known to occur in several cv3 chondrites we report petrologic chemical and oxygen isotopic data on examples from allende leoville and vigarano the allende inclusions comprise a petrographic sequence ranging from a type which contains chondrules and refractory inclusions and resembles cv3 or co3 chondrites to a type which contains porous aggregates of iron rich olivine oxygen isotopic compositions correlate with the sequence chondrule rich inclusions have compositions similar to the host meteorite bulk values whereas olivine aggregate rich inclusions have more 16o depleted compositions chemical compositions on the other hand do not correlate with the petrographic sequence the dark inclusions are all systematically enriched in iron and depleted in potassium and sodium relative to their host meteorites the inclusions appear to be fragments of cv3 parent bodies which were processed to different degrees prior to their incorporation as clasts into allende leoville and vigarano the processing homogenized olivine compositions presumably through heating and also involved oxygen exchange with 16o poorer surroundings either parent body metamorphism or nebular heating might have produced the petrographic and isotopic sequences however the most 16o depleted inclusions also have layered silicate rims surrounding them which are better attributed to gas solid reactions than parent body processes in particular andradite is abundant in the rims which implies that the rims grew under conditions significantly more oxidizing than those likely to have occurred on a cv3 parent body at least part of the processing therefore appears to have taken place prior to final accumulation of the material when the fragments were dispersed in the nebula the evidence for coupled oxidation and 16o depletion in the nebula suggests that other features of the cv3 group such as the oxidized and reduced subgroups ferrous rims on forsteritic olivines and coarse grained rims on chondrules may have been established by similar gas solid reactions prior to the final assembly of the meteorites

comparison of sediment sound velocity functions from conjugate margins a comparison of velocity functions from 15 regions within the conjugate margins of the norwegian greenland sea southeast indian ocean north atlantic and south atlantic ocean shows that velocity functions are not significantly different across most conjugate margins one major exception is the segment from the blake plateau to new england in the western north atlantic and its counterpart in northwest africa here the velocity gradients are consistently steeper on the african side compared with those on the north american side the reason for this unexpected difference was sought in the geologic literature of the two margins published studies of these two margins show that although total subsidence and sediment thickness of each of the margins are about equal the older beds pre cenozoic are much thicker on the african side this fundamental difference in depositional history seems to be the major cause of the difference in velocity profiles possible differences in the distribution of salt along the margins of africa and north america are not considered a likely source for the trans atlantic differences in the velocity functions the north atlantic data therefore illustrate that velocity increases more rapidly with depth in sections biased toward greater proportions of older beds that is sedimentation rates decrease as the basin ages these studies also reveal that sound velocity profiles are sensitive to the early conditions of deposition on passive margins

possible melting produced chondrule destruction in nwa 6604 ck4 chondrite in analyzing a thin section of the nwa 6604 ck4 meteorite only altered chondrules and various components that are probably left behind the destruction of former chondrules can be observed we suggest that melting grain size decrease resorption of the original chondrules and crystallization of opaque minerals were the main processes that destroyed the chondrules four different events could be identified as having occurred during this alteration first opaques crystallized along former fractures producing chains of separated grains later opaques and ca rich minerals crystallized together in veins and large melt pockets this was the strongest recrystallization phase involving the largest volume of melt this occurred along different fractures than the first phase above during the third phase only ca rich plagioclase crystallized along thin veins and in a fourth phase fractures formed again partly along those formed during the second phases but without substantial mineral infill two simple possible case models should be considered for this meteorite alteration by purely impact driven processes or mainly by melt driven processes although for ck4 chondrites the shock produced alteration driven by impact is the more accepted and widespread approach melting is also compatible with the observed textural characteristics of chondrule destruction during melting recrystallization took place producing iron rich minerals earlier and ca si rich ones later the penetration of melts into veins contributed in the chondrule destruction the stress directions also changed during these alterations and minerals that formed later filled differently oriented fractures than the earlier ones from our observations we favor a view where heat driven melting and recrystallization produced the destruction and uniform mineralogy in the sample

the mineral chemistry and origin of inclusion matrix and meteorite matrix in the allende cv3 chondrite the two textural varieties of olivine rich allende inclusions rimmed and unrimmed olivine aggregates consist primarily of a porous fine grained mafic constituent inclusion matrix that differs from the opaque meteorite matrix of cv3 chondrites by being relatively depleted in sulfides metal grains and perhaps carbonaceous material olivine is the most abundant mineral in allende inclusion matrix clinopyroxene nepheline sodalite and ti al pyroxene occur in lesser amounts olivine in unrimmed olivine aggregates type 1a inclusions is ferrous and has a narrow compositional range fo50 65 olivine in rimmed olivine aggregates type 1b inclusions is on average more magnesian with a wider compositional range fo53 96 olivine grains in the granular rims of type 1b inclusions are zoned with magnesian cores fo 80 and ferrous rinds fo 70 ferrous olivines fo 65 in both varieties of inclusions commonly contain significant amounts of al2o3 as much as 0 7 wt cao as much as 0 4 wt and tio2 as much as 0 2 wt refractory elements that probably occur in submicroscopic inclusions of ca al ti rich glass rather than in the olivine crystal structure defocussed beam analyses of allende matrix materials demonstrate that 1 inclusion matrix in type 1a inclusions is more enriched in olivine and feo than inclusion matrix in the cores of type 1b inclusions 2 opaque matrix materials are depleted in feldspathoids and enriched in sulfides and metal grains relative to inclusion matrix 3 the bulk compositions of type 1a and type 1b inclusions overlap and 4 excluding sulfides and metal the bulk compositions of allende matrix materials cluster in a complementary pattern around the bulk composition of c1 chondrites inclusion matrix and meteorite matrix in allende and other cv3 chondrites are probably relatively primitive nebular material but a careful evaluation of the equilibrium condensation model suggests that these matrix materials do not consist of crystalline phases that formed under equilibrium conditions in a relatively cool gas of solar composition allende inclusion matrix is interpreted as an aggregate of condensates that formed under relatively oxidizing non equilibrium conditions from supercooled supersaturated vapors produced during the vaporization of interstellar dust by aerodynamic drag heating in the solar nebula cv3 meteorite matrix contains in addition a proportion of interstellar material that was heated but not vaporized in the nebula granular olivine in rimmed olivine aggregates may have formed during the recrystallization and incipient melting of aggregates of inclusion matrix in the nebula the mineral chemistry of matrix olivine in allende seems to have been established by three different processes non equilibrium vapor solid condensation recrystallization and partial melting in the nebula and femg equilibration without textural homogenization in the meteorite parent body

coarse grained chondrule rims in type 3 chondrites abstract relatively coarse grained rims occur around all types of chondrules in type 3 carbonaceous and ordinary chondrites those in h l ll3 chondrites are composed primarily of olivine and low ca pyroxene those in cv3 chondrites contain much less low ca pyroxene average grain sizes range from 4 m in h l ll3 chondrites to 10 m in cv3 chondrites such rims surround 50 10 and 1 of chondrules in cv3 h l ll3 and co3 chondrites respectively but are rare 1 around cv3 ca al rich inclusions rim thicknesses average 150 m in h l ll3 chondrites and 400 m in cv3 chondrites the rims in h l ll3 chondrites are composed of material very similar to that which comprises darkzoned chondrules and recrysiallized matrix dark zoned chondrules and coarse grained rims probably formed in the solar nebula from clumps of opaque matrix material heated to sub solidus to sub liquidus temperatures during chondrule formation mechanisms capable of completely melting some material while only sintering other material require steep thermal gradients suitable processes are lightning reconnecting magnetic field lines and possibly aerodynamic drag heating cv chondrites may have formed in a region where the chondrule formation mechanism was less efficient probably at greater solar distances than the ordinary chondrites the lesser efficiency of heating could be responsible for the greater abundance of coarse grained rims around cv chondrules alternatively cv chondrules may have suffered fewer particle collisions prior to agglomeration

spatial characteristics of sediment trace metals in an eastern boundary upwelling retention area st helena bay south africa a hydrodynamic biological pump hypothesis st helena bay a retention zone located in the southern benguela upwelling system is an important fish nursery however it suffers from seasonal bottom water hypoxia causing major economic losses anoxic conditions are linked to sulfide fluxes from bottom sediments defined by a high sedimentation rate of organic matter it is proposed that trace metals may play an important role in alleviating part of the ecological stress by forming sulfide complexes in such systems a spatially intensive data set of sediment biogeochemical characteristics showed that poc and trace metals cr cu zn ni etc accumulated in the central zone of the bay furthermore trace metal concentrations were strongly correlated with both poc and al to explain the observed biogeochemical relationships in st helena bay we propose a hypothesis that links the upwelling retention hydrodynamics primary productivity and sediment trace metal distribution trace metals are incorporated into phytoplankton cells in the euphotic zone but rapidly sediment along with particulate organics on their senescence both the biological pump and the dispersion of particulates are primarily controlled by the hydrodynamics prevalent within st helena bay which also govern the retention zone in the shadow of one of the major upwelling cells the dynamics of entrainmentestratification drives the productivity while a residual cyclonic gyre concentrates the surface productivity within the bay bed shear stresses spatially constrain the accumulation of biogenic organic matter which governs the trace metal biogeochemistry of the sediments along a narrow terrigenous mud belt 2005 elsevier ltd all rights reserved

chondritic meteorites and the solar nebula when the solar system formed the abundance pattern of nonvolatile elements in chondrites corresponds closely to abundance patterns in the atmo spheres of the sun and many stars in the galaxy cameron 1982 indi cating that chondrites are condensed samples of undifferentiated cosmic matter they are specimens of planetary material in very nearly the same state it assumed when the planets were first formed in particular they have never experienced planetary melting and the chemical fractionations that attend igneous processes chondrites have broadly ultramafic compositions dodd 1981 con sistent with the predominance ofmg si and fe in the elemental abundance pattern of undifferentiated cosmic material the chief mineral constituents of chondrites are olivine pyroxene and ni fe metal their textures are aggregational they consist of mixtures in various proportions of three particulate components a chondrules are more or less spheroidal ultra mafic igneous bodies roughly a millimeter in dimension they are very abundant 30 70 by volume in the chondrites that this article discusses and tend to dominate the textural patterns of their hosts b refractory inclusions ri are more irregular in shape and range in size from several centimeters down to the limit of microscopic visibility most of them contain enhanced concentrations of the most involatile elements e g ai i the us government has the right to retain a nonexclusive royalty free license in and to any copyright covering this paper

empirical reflection travel time versus depth and velocity versus depth functions for the deep sea sediment column numerous correlations of one way reflection travel times and depths to reflecting horizons have been proposed in the initial reports of the deep sea drilling project dsdp having carefully reviewed proposed correlations we selected 233 correlated depths ranging from 27 m to 1 4 km and one way travel times ranging from 0 02 to 0 7 s from 154 dsdp sites worldwide assuming that the velocity depth function for deep sea sediments can be approximated by an exponential form we have used these data to establish statistically well constrained global models relating depth to travel time and velocity to depth there is remarkably little scatter in the data based on nonlinear least squares fits the best depth time function is z km 3 03 1n 1 0 52t s the rms error in depth is 26 m the corresponding average velocity depth function is v km s 1 59exp 0 33z we estimate that the real site to site variability of velocities at depth is less than 0 20 km s any dependence of velocity on composition is below the resolution of the data and available evidence suggests that age has no significant effect these results imply that to a depth of 1 4 km the physical state of sediments depends on in situ overburden pressure and temperature which are related to depth of burial and that chemical and mechanical equilibrium is achieved in a period of time that is geologically short our results are consistent with laboratory measurements of p wave velocities in deep sea sediments but velocity depth functions for terrigenous and calcareous sections derived from sonobuoy wide angle reflection surveys are incompatible with the time and depth data and overestimate velocities by as much as 10 and 30 respectively these systematic errors may result from the fact that the marked anisotropy of deep sea sediments is neglected in the interpretation of reflection data

an assessment of ocean margin anaerobic processes on oceanic alkalinity budget 1 recent interest in the ocean s capacity to absorb atmospheric co2 and buffer the accompanying ocean acidification has prompted discussions on the magnitude of ocean margin alkalinity production via anaerobic processes however available estimates are largely based on gross reaction rates or misconceptions regarding reaction stoichiometry in this paper we argue that net alkalinity gain does not result from the internal cycling of nitrogen and sulfur species or from the reduction of metal oxides instead only the processes that involve permanent loss of anaerobic remineralization products i e nitrogen gas from net denitrification and reduced sulfur i e pyrite burial from net sulfate reduction could contribute to this anaerobic alkalinity production our revised estimate of net alkalinity production from anaerobic processes is on the order of 4 5 tmol yr 1 in global ocean margins that include both continental shelves and oxygen minimum zones significantly smaller than the previously estimated rate of 16 31 tmol yr 1 in addition pyrite burial in coastal habitats salt marshes mangroves and seagrass meadows may contribute another 0 1 1 1 tmol yr 1 although their long term effect is not yet clear under current changing climate conditions and rising sea levels finally we propose that these alkalinity production reactions can be viewed as charge transfer processes in which negative charges of nitrate and sulfate ions are converted to those of bicarbonate along with a net loss of these oxidative anions

petrographic studies of refractory inclusions from the murchison meteorite textural and mineral chemical data on freeze thaw disaggregated refractory inclusions from the murchison meteorite are reported the data were obtained with neutron activation analysis sem and spectroscopy the study revealed corundum bearing inclusions spinel hibonite aggregates and spherules and spinel pyroxene and elivine pyroxene inclusions one of the three spinel pyroxene forsterite rich inclusions had an amoeba shaped spinel pyroxene core implying vapor to solid condensation and therefore crystallization from a melt it is concluded that the meteorite formation encompassed diverse nebular materials and that further studies of the meteorite will enhance the data base on the planetary nebular processes

hydrothermal experiments on alteration of ca al rich inclusions cais in carbonaceous chondrites implication for aqueous alteration in parent asteroids carbonaceous chondrites contain ca al rich inclusions cais which consist mainly of refractory minerals including gehlenite spinel perovskite and hibonite which are predicted to be the first phases formed from early solar nebula on the basis of thermodynamic calculations however many cais contain secondary minerals such as nepheline calcite and phyllosilicates the formation process of secondary minerals in cais is still controversial whether they were produced by the reaction with solar nebula or by aqueous alteration in parent asteroids we performed hydrothermal experiments on gehlenite spinel and diopside which are common in cais in carbonaceous chondrites to study aqueous alteration in parent asteroids mixtures of gehlenite with sio2 and or al2o3 and those of sio2 with al2o3 were also employed to study products of these systems which have a close relationship to crystallization of secondary minerals in cais in fluid in parent asteroids hydrogrossular calcite and amorphous al si were obtained from gehlenite by hydrothermal experiments whereas both spinel and diopside escaped alteration suggesting that gehlenite is the weakest mineral among these refractory minerals against alteration this result is consistent with observation of cais analcime nepheline hydrate and tobermorite were obtained from the runs for mixtures of gehlenite with sio2 whereas the products from mixtures of al2o3 with sio2 were analcime nepheline hydrate and hydrosodalite these results suggest that the alteration process of gehlenite is as follows 1 gehlenite was dissolved by fluid in chondrite parent asteroids to release ca al and si from the surface 2 co32 in fluid reacted with ca to crystallize calcite 3 na al and si in fluid crystallized nepheline hydrate hydrosodalite and or analcime 4 ca al and si in fluid crystallized hydrogrossular without co32 and excess ca and si crystallized ca si hydrate such as tobermorite heating experiments on several minerals obtained through hydrothermal experiments were also performed to study thermal metamorphism in parent asteroids hydrogrossular was converted into hydrogrossular with a lower h2o content and analcime and nepheline hydrate were converted into nepheline tobermorite is known to be converted into wollastonite with increasing temperature the results of experimental studies suggest that most secondary minerals found in cais in carbonaceous chondrites were produced from gehlenite by aqueous alteration and the subsequent thermal metamorphism in parent asteroids

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

in situ acoustic properties of pelagic carbonate sediments on the ontong java plateau the ontong java plateau with its thick capping sequence of cretaceous and cenozoic pure pelagic carbonate sediments forms an ideal setting for the study of the acoustic properties of this lithology on an oceanic rise borehole logs recorded on deep sea drilling project leg 89 at site 586 provided detailed data on in situ acoustic properties of pleistocene to early miocene sediments to a depth of 623 m below seafloor comparison of these logging results and the sonobuoy based results of johnson et al 1978 with previous laboratory measurements from the ontong java plateau shows that velocity depth functions determined from the logging and sonobuoy methods are concordant but diverge significantly from functions derived from laboratory measurements log densities and compressional velocities exceed those measured by laboratory techniques the density discrepancy is strongly influenced by laboratory method the differences between log and laboratory compressional velocities are greater than and extend to greater depths than those between densities these differences can be attributed to reductions in the frame bulk modulus and dynamic rigidity caused by the removal of overburden pressure in the absence of significant porosity rebound agreement of site 586 log velocities with velocities derived from the earlier sonobuoy measurements across the plateau argues for the interpretation that both methods measure in situ values the disagreement between the site 586 log results and the sonobuoy results with both the empirical velocity depth function of carlson et al 1986 and the empirical velocity porosity function of raymer et al 1980 supports the conclusion that pelagic carbonate sediments on oceanic plateaus and rises have unique acoustic properties primarily arising from the presence of intraparticle porosity and should not be grouped with other oceanic lithologies in acoustic modeling studies

pregraphitic and poorly graphitised carbons in porous chondritic micrometeorites abstract two forms of crystalline carbon in porous chondritic micrometeorites w7029e5 u2011c2 and u2022c7 c8 are mixed layered pregraphitic carbons with c c h o n at 0 45 this bulk composition is inferred from the presence of three groupings of d 002 basal spacings at 0 45 nm 0 37 nm and 0 348 nm mixed layered carbons represent incomplete carbonisation and graphitisation of precursor material in u2022c7 c8 carbonisation mostly involved volatile loss the formation of pregraphitic carbons indicates a sustained thermal regime in parent bodies of these micrometeorites i e short period comets outer belt asteroids or protocomet nuclei temperatures of the sustained thermal regime remain unspecified but carbon reactions were probably facilitated by catalytic support from layer silicates in these samples poorly graphitised carbon in u2022c7 c8 formed during a transient thermal event which is most likely flash heating during micrometeoroid deceleration in the earth s atmosphere

the nature and origin of type b1 and b2 caal rich inclusions in the allende meteorite abstract the type b ca al rich inclusions in the allende carbonaceous chondrite form a continuous range from the mineralogically concentrically zoned b1 subtype to the unzoned b2 subtype these subtypes differ in i structure texture grain size and shape ii mineralogical proportions and compositions iii accessory mineralogy iv relative abundance of spinel framboids v rim layering vi major element chemistry and vii degree of secondary alteration these differences together with observations on the crystallization of synthetic melts suggest that the b1 inclusions crystallised relatively rapidly from molten parental material while b2 types crystallised relatively slowly close to the solidus from material that had not been completely melted the same data are used to construct an evaporative residue model for the origin of the parental type b materials in the model dust in the protosolar nebula was heated with removal of more volatile elements leaving completely melted type b1 residues at the highest temperatures and incompletely melted less highly evaporated type b2 residues at lower temperatures

the blue angel i the mineralogy and petrogenesis of a hibonite inclusion from the murchison meteorite a detailed mineralogie chemical and petrologic study of the blue angel a relatively large 1 5 mm hibonite containing inclusion from the murchison meteorite was performed in an attempt to understand the mechanisms of formation and modification of hibonite rich inclusions the blue angel inclusion is composed of roughly equal amounts of hibonite and calcite with minor amounts of spinel perovskite diopside and an fe rich silicate the inclusion can be divided into three roughly concentric zones a hibonite rich core a calcite rich mantle and a spinel rich layered rim the mineral chemistry and petrography of the blue angel are consistent with a three stage formation history 1 an early stage of nebular condensation which produced the hibonite perovskite and spinel 2 a moderate temperature stage of aqueous alteration and metamorphism occurring on a small planetary body containing co 2 and h 2o during which calcite was formed in the inclusion and 3 the final emplacement of the blue angel into its present position in murchison the study of the blue angel indicates that extensive alteration of ca al rich inclusions cai may have occurred by aqueous alteration and thermal metamorphism followed by explosive mixing processes on a parent body such metamorphic reactions may involve formation and destruction of phases such as melilite and diopside which have been previously thought to be primary condensates the mechanisms proposed for the formation and modification of the blue angel help to explain the secondary phases and oxygen isotope anomalies found in many cai and eliminate the need for invoking kinetically complicated back reactions at very low pressures with a cool part of the solar nebula the contribution of planetary metamorphism in the formation and alteration of cai must be considered along with nebular processes in order to understand the formation of carbonaceous chondrites

interplanetary dust particles collected in the stratosphere observations of atmospheric heating and constraints on their interrelationships and sources abstract the majority of the interplanetary dust particles idps collected in the stratosphere belong to one of three major classes the first two dominated by the anhydrous minerals olivine and pyroxene and the third by hydrous layer lattice silicates infrared spectroscopy and transmission electron microscopy studies show that the different idp classes represent different types of dust that exist as individual particles in interplanetary space the majority of the collected idps smaller than 30 m in diameter in the layer lattice silicate and pyroxene classes appear not to have been heated to temperatures above 600 c during atmospheric entry the relatively low maximum temperatures experienced by these idps during atmospheric entry imply that they arrive at the top of the atmosphere with low geocentric encounter velocities this limits the possible encounter trajectories for these particles to relatively circular prograde orbits as a result it is unlikely that these idps are from earth crossing comets or asteroids asteroids and comets having low inclinations and perihelia outside 1 2 ua appear to be the best candidates for the parent bodies of the pyroxene and layer lattice silicate particles chemical and mineralogical information suggests that the pyroxene rich idps are from comets and layer lattice silicate rich idps are from asteroids the collected idps dominated by olivine appear to include a larger fraction of particles heating above 600 c suggesting that these particles were captured from more eccentric orbits this and the observation of the infrared spectral features of olivine in several comets suggest these particles have a cometary origin since much of the collected dust has apparently been captured from nearly circular prograde orbits and since there are no appropriate parent bodies presently in such orbits these results provide an experimental confirmation that the poynting robertson effect exists as a nongravitational force important in the orbital evolution of dust in the solar system

chondrules matrix and coarse grained chondrule rims in the allende meteorite origin interrelationships and possible precursor components bulk compositions of 20 chondrules 13 coarse grained chondrule rims and two composite samples of matrix material from cv3 allende were determined by instrumental neutron activation analysis three rare nonporphyritic cv chondrules from allende leoville and vigarano were analyzed by broad beam electron microprobe analysis chondrule precursor components deduced from chondrule compositions are characterized by 1 refractory and semi refractory lithophiles with low feo 2 common siderophiles and chalcophiles 3 common to slightly volatile lithophiles si cr mn and modal pyroxene with moderately high feo feo mgo 4 moderately volatile siderophiles and 5 alkalies these precursor components can be explained by plausible processes occurring in the solar nebula the precursor components of coarsegrained rims are apparently the same as those of chondrules these components differ from those inferred previously for oc eh or cm co chondrules in general the compositions of coarse grained rims are more similar to the mean chondrule composition than to those of the chondrules they enclose rim siderophile contents are generally 2 5x greater than those in the chondrules and 0 5 to 2x those in bulk allende rims as a group are more homogeneous than chondrules suggesting that rims formed from finer grained precursors several chondrules and rims have fractionated rare earth patterns and may have been affected by metamorphism the enclosure of some coarse grained rims by fine grained matrix like rims that are almost certainly of nebular origin indicates that coarse grained rims were also formed in the nebula two matrix samples are similar in composition to some coarse grained rims suggesting that matrix was derived from similar compositional reservoirs of nebular dust chondrules with coarse grained rims were reheated in space following the accretion of dusty coatings this restricts plausible chondrule forming mechanisms to those that allow multiple nebular heating events

progressive alteration in cv3 chondrites more evidence for asteroidal alteration abstract the oxidized cv3 chondrites can be divided into two major subgroups or lithologies bali like cv3oxb and allende like cv3oxa in which chondrules calcium aluminum rich inclusions cais and matrices show characteristic alteration features weisberg et al 1997 krot et al 1997d kimura and ikeda 1997 the cv3oxb lithology is present in bali kaba parts of the mokoia breccia and possibly in grosnaja and allan hills alh 85006 it is characterized by the presence of the secondary low ca phyllosilicates saponite and sodium phlogopite magnetite ni rich sulfides fayalite fa 90 ca fe rich pyroxenes fs10 50wo45 50 and andradite phyllosilicates replace primary ca rich minerals in chondrules and cais which suggests mobilization of ca during aqueous alteration magnetite nodules are replaced to various degrees by fayalite ca fe rich pyroxenes and minor andradite fayalite veins crosscut fine grained rims around chondrules and extend into the matrix thermodynamic analysis of the observed reactions indicates that they could have occurred at relatively low temperatures 300 c in the presence of aqueous solutions oxygen isotopic compositions of the coexisting magnetite and fayalite plot close to the terrestrial fractionation line with large 18ofayalite magnetite fractionation 20 we infer that phyllosilicates magnetite fayalite ca fe rich pyroxenes and andradite formed at relatively low temperatures 300 c by fluid rock interaction in an asteroidal environment secondary fayalite and phyllosilicates are virtually absent in chondrules and cais in the cv3oxa lithology which is present in allende and its dark inclusions axtell alha81258 alh 84028 lewis cliff lew 86006 and parts of the mokoia and vigarano breccias instead secondary nepheline sodalite and fayalitic olivine are common fayalitic olivine in chondrules replaces low ca pyroxenes and rims and veins forsterite grains it also forms coarse lath shaped grains in matrix secondary ca fe rich pyroxenes are abundant we infer that the cv3oxa lithology experienced alteration at higher temperatures than the cv3oxb lithology the presence of the reduced and cv3oxa lithologies in the vigarano breccia and cv3oxa and cv3oxb lithologies in the mokoia breccia indicates that all cv3 chondrites came from one heterogeneously altered asteroid the metamorphosed clasts in mokoia krot and hutcheon 1997 may be rare samples of the hotter interior of the cv asteroid we conclude that the alteration features observed in the oxidized cv3 chondrites resulted from the fluid rock interaction in an asteroid during progressive metamorphism of a heterogeneous mixture of ices and anhydrous materials mineralogically similar to the reduced cv3 chondrites

mineralogy and petrography of amoeboid olivine aggregates from the reduced cv3 chondrites efremovka leoville and vigarano products of nebular condensation accretion and annealing amoeboid olivine aggregates aoas from the reduced cv chondrites efremovka leoville and vigarano are irregularly shaped objects up to 5 mm in size composed of forsteritic olivine fa 50 melting we infer that aoas are aggregates of high temperature nebular condensates which formed in cai forming regions and that they were absent from chondrule forming regions at the time of chondrule formation the absence of low ca pyroxene and depletion in moderately volatile elements mn cr na k suggest that aoas were either removed from cai forming regions prior to condensation of these elements and low ca pyroxene or gas solid condensation of low ca pyroxene was kinetically inhibited

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

comparing wild 2 particles to chondrites and idps we compare the observed composition ranges of olivine pyroxene and fe ni sulfides in wild 2 grains with those from chondritic interplanetary dust particles idps and chondrite classes to explore whether these data suggest affinities to known hydrous materials in particular wild 2 olivine has an extremely wide composition range from fa096 with a pronounced frequency peak at fa1 the composition range displayed by the low calcium pyroxene is also very extensive from fs48 to fs0 with a significant frequency peak centered at fs5 these ranges are as broad or broader than those reported for any other extraterrestrial material wild 2 fe ni sulfides mainly have compositions close to that of fes with less than 2 atom ni to date only two pentlandite grains have been found among the wild grains suggesting that this mineral is not abundant the complete lack of compositions between fes and pentlandite with intermediate solid solution compositions suggests but does not require that fes and pentlandite condensed as crystalline species i e did not form as amorphous phases which later became annealed while we have not yet observed any direct evidence of water bearing minerals the presence of ni bearing sulfides and magnesium dominated olivine and low ca pyroxene does not rule out their presence at low abundance we do conclude that new investigations of major and minorelement compositions of chondrite matrix and idps are required

petrology and origin of amoeboid olivine aggregates in cr chondrites amoeboid olivine aggregates aoas are irregularly shaped fine grained aggregates of olivine and ca al rich minerals and are important primitive components of cr chondrites the aoas in cr chondrites contain feni metal and some aoas contain mn rich forsterite with up to 0 7 mno and mn fe ratios greater than one additionally aoas in the cr chondrites do not contain secondary phases nepheline and fayalitic olivine that are found in aoas in some cv chondrites the aoas in cr chondrites record a complex petrogenetic history that included nebular gas solid condensation reaction of minerals with the nebular gas small degrees of melting and sintering of the assemblage a condensation origin for the mn rich forsterite is proposed the mn rich forsterite found in idps unequilibrated ordinary chondrite matrix and aoas in cr chondrites may have had a similar origin a type a calcium aluminum rich inclusion cai with an aoa attached to its wark lovering rim is also described this discovery reveals a temporal relationship between aoas and type a inclusions additionally a thin layer of forsterite is present as part of the wark lovering rim revealing the crystallization of olivine at the end stages of the wark lovering rim formation the ca al rich nodules in the aoas may be petrogenetically related to the ca al rich minerals in wark lovering rims on type a cais aoas are chondrite components that condensed during the final stage of wark lovering rim formation but in general were temporally spatially or kinetically isolated from reacting with the nebula vapor during condensation of the lower temperature minerals that were commonly present as chondrule precursors

dynamic pyrometamorphism during atmospheric entry of large 10 micron pyrrhotite fragments from cluster idps petrological changes in ni free and low ni pyrrhotite and much less in pentlandite during atmospheric entry flash heating of the sulfide idps l2005e40 l2005c39 and l2006a28 support 1 ferrous sulfide oxidation with vacancy formation and fe 3 ordering and 2 fe oxide formation and sulfur vapor loss through abundant vesicles melting of metastable chondritic aggregate materials at the idp surface has occurred all changes e g formation of a continuous maghmite rim proceeded as solid state reactions at a peak heating temperature of 700 c this temperature in combination with particle size and density suggest a 10 km s 1 entry velocity the idps probably belonged to cluster idps that entered the atmosphere with near earth or earth crossing asteroid velocities they could be debris from extinct or dormant comet nuclei which is consistent with shock comminution of pyrrhotite in these idps

laboratory hydration of condensed magnesiosilica smokes with implications for hydrated silicates in idps and comets samples of silica rich and mgo rich condensed amorphous magnesiosilica smokes were hydrated to monitor systematic mineralogical and chemical changes as a function of time and temperature controlled by their unique metastable eutectic compositions their porous texture and the ultrafine nanometer grain size of all entities at water supersaturated conditions proto phyllosilicates formed by spinodal type homogeneous nucleation their formation and subsequent growth was entirely determined by the availability of water via pore spaces inherited from the original smokes and the textural continuity of magnesiosilica material with a mostly smectite dehydroxylate composition the results may have implications for the hydration of proto ci material the presence of rare periclase and brucite in primitive solar system bodies and the pervasiveness of hydrated amorphous magnesiosilica dust and saponite proto phyllosilicates in icy protoplanets such as comet nuclei

the interstellar dust as a precursor of ca al rich inclusions in carbonaceous chondrites abstract 1 the observed anomalies in meteoritic oxygen isotope compositions are not due to an incomplete mixing of several dust or gas plus dust components in the solar nebula if they were other elements would display similar anomalies the fun inclusions in allende appear to be exceptions to this premise 2 the anomalies must therefore stem from differing degrees of incomplete exchange of oxygen isotopes between the primordial gas and dust components of the nebula the dust is more likely to have been the 16 o enriched component 3 since the isotopic difference between dust and gas probably could not have been preserved if the dust was ever completely vaporized in the nebula the ca al rich inclusions cai s in carbonaceous chondrites are unlikely to be condensates but instead are distillation residues 4 if so the observed depletion of super refractory elements in the group ii cai s cannot have been accomplished by fractional condensation in the solar nebula 5 then this depletion and a number of other properties of the components of primitive meteoritic material must be relics of pre solar system fractionations among different populations of interstellar dust grains

physicochemical isotope anomalies isotopic composition of refractory elements can be modified by physical processes such as distillation and sputtering in unexpected patterns distillation enriches the heavy isotopes in the residue and the light isotopes in the vapor however current models appear to be inadequate to describe the detailed mass dependence in particular for large fractionations coarse and fine grained inclusions from the allende meteorite exhibit correlated isotope effects in mg both as mass dependent fractionation and residual anomalies this isotope pattern can be duplicated by high temperature distillation in the laboratory a ubiquitous property of meteoritic inclusions for mg as well as for most of the other elements where measurements exist is mass dependent fractionation in contrast terrestrial materials such as microtektites tektite buttons as well as lunar orange and green glass spheres have normal mg isotopic composition a subset of interplanetary dust particles labelled as chondritic aggregates exhibit excesses in sup 26 mg and deuterium anomalies sputtering is expected to be a dominant mechanism in the destruction of grains within interstellar dust clouds an active proto sun as well as the present solar wind and solar flare flux are of sufficient intensity to sputter significant amounts of material laboratory experiments in mg show widespread isotope effects including residual supmore 26 mg excesses and mass dependent fractionation it is possible that the sup 26 mg excesses in interplanetary dust is related to sputtering by energetic solar wind particles the implication if the laboratory distillation and sputtering effects are discussed and contrasted with the anomalies in meteoritic inclusions the other extraterrestrial materials the authors have access to less

evolution of caal rich bodies in the earliest solar system growth by incorporation abstract many type b ca al rich inclusions cai s in the allende carbonaceous chondrite contain two types of spinel structures framboids and palisades framboids are clumps of spinel grains generally in situ by solid state growth processes palisades are texturally different and consist of ovoid shells of spinel grains that appear in thin sections as long arcs or rings with diameters ranging from 50 m up to 2 cm no in situ formation process seems able to explain the variety of sizes and morphologies of palisades nor the different compositions and textures of the enclosed and enclosing materials we therefore suggest that palisades are the spinel rims of smaller earlier formed type b cai s that were incorporated into other cai material in various ways by capture into liquid drops by solid condensate overgrowths and by the partial melting or welding of agglomerates containing the bodies as some type b bodies have been found inside type a host material it appears that in at least some regions and probably generally type a cai s formed after type b we propose that type b cai s are residues from the heating and incomplete evaporation of interstellar dust during the accretion of the protosolar nebula and that type a cai s are later condensates from completely evaporated dust whose exotic 16 o rich component became more diluted in the gas phase

epitaxial growth of nanophase magnetite in martian meteorite allan hills 84001 implications for biogenic mineralization crystallographic relationships between magnetite sulfides and carbonate rosettes in fracture zones of the allan hills alh 84001 martian meteorite have been studied using analytical electron microscopy we have focused on those magnetite grains whose growth mechanisms can be rigorously established from their crystallographic properties individual magnetite nanocrystals on the surfaces of carbonates are epitaxially intergrown with one another in stacks of single domain crystals other magnetite nanocrystals are epitaxially intergrown with the surfaces of the carbonate substrates the observed magnetite carbonate hkl miller indices orientation relationships are 1 1 3 m 1 1 0 c and 1 1 1 m 0 0 3 c with lattice mismatches of approximately 13 and approximately 11 respectively epitaxy is a common mode of vapor phase growth of refractory oxides like magnetite as is the spiral growth about axial screw dislocations previously observed in other magnetite nanocrystals in alh 84001 epitaxy rules out intracellular precipitation of these magnetites by martian organisms provides further evidence of the high temperature 120 degrees c inorganic origins of magnetite in alh 84001 and indicates that the carbonates also have been exposed to elevated temperatures

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

mineralogy of interplanetary dust particles from the olivine infrared class analytical electron microscopy observations establish that olivine is abundant and the predominant silicate phase in threeinterplanetary dust particles idps from the olivine infrared spectral category two of the particles have microstructures resembling those of most non hydrous chondritic idps consisting of micron to sub micron grains together with a matrix composed of amorphous carbonaceous material and sub 500grains in addition to olivine theseparticles respectively contain enstatite and magnetite and pentlandite plus ca rich clinopyroxene the third idp consists mostly of olivine and pyrrhotite with little or no matrix material olivine grains in this particle contain prominent solar flare ion tracks with densities corresponding to a space exposure age between 103 to 105 years although the three particles have olivine rich mineralogies in common other aspects of their mineralogies and microstructures suggest that they experienced different formation histories the differences between the particles indicate that the olivine infrared spectral category is a diverse collection of idps that probably incorporates several genetic groups

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

granoblastic olivine aggregates as precursors of type i chondrules an experimental test abstract chondrule formation models involving precursors of granoblastic olivine aggregates goa of either planetesimal or nebular origin have recently been proposed we have therefore conducted chondrule simulation experiments using mixtures of 100 h thermally annealed goa and an en to test the viability of goa as predecessors of porphyritic olivine po chondrules isothermal runs of less than 5 min at 1350 1550 c result in goa disaggregation and fe mg exchange runs of 0 5 4 h show textures superficially similar to granular and po chondrules but with reversely zoned olivine charges isothermally heated at 1550 c for 1 and 4 h before being cooled at 10 and 100 c h undergo olivine crystallization and yield classical po textures although most evidence of origin from goa is erased the cores of normally zoned euhedral crystals are relict as phenocrysts in type i chondrules can be relict such chondrules could have experienced similar peak temperatures to those of type ii chondrules chondrules containing goa with olivine triple junctions resemble experimental charges heated for minutes at temperatures between 1350 and 1450 c and type i chondrules with subhedral to anhedral olivine plus goa relicts resemble charges heated at the same temperatures but for longer duration type i chondrules with a mass of granular olivine or irregular anhedral olivine grains in the center and much glass nearer the margin on the other hand require limited heating at high temperature 1550 c while type i chondrules with euhedral olivines resemble charges heated at 1550 c for 4 h the majority of type i chondrules in cv chondrites display evidence of derivation from goa many finer grained chondrules in cr and uoc on the other hand could not have been derived from such coarse grained precursors but could have formed from fine grained dustballs as stipulated in the standard paradigm thus both goa and dustballs represent viable chondrule precursors of coarser and finer grained type i po chondrules respectively

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

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

characteristics of the surface boundary layer important to the development of red tide on the southern namaqua shelf of the benguela upwelling system the southern namaqua shelf north of the cape columbine upwelling center is particularly prone to red tide two influences of the surface boundary layer on the development of red tide in this area were investigated the dynamics of the upper mixed layer in determining phytoplankton community composition and the role of mesoscale circulation in bloom concentration and transport two survey periods 18 february 11 march 2000 and 13 30 march 2001 are reported during which red tide dominated by the dinoflagellate gyrodinium zeta formed in the area a high degree of concordance between characteristics of stratification and groupings of phytoplankton demonstrated the importance of the upper mixed layer in determining species or life form selection and development ordination of across shelf phytoplankton samples revealed a consistent banded pattern created by a wind induced upwelling plume tending to isolate a nearshore zone from an offshore domain thereby creating an area of retention on the coastal side of the plume favoring development of dinoflagellate blooms the appearance of red tide was clearly associated with increasingly stratified conditions driven by alongshore flow from the north following periods of wind relaxation and consequent reversal of surface currents the southern benguela upwelling system forms part of one of four major eastern boundary current regions of the world ocean here a range of dinoflagellate species is responsible for toxic or otherwise harmful blooms pitcher and calder 2000 these blooms often referred to as red tides are common during the latter part of the upwelling season when the wind moderates and insolation is still strong causing seasonal stratification to increase their accumulation inshore and the formation of red tide is thought to be driven by synoptic weather patterns which dictate the across shelf and alongshore movement of blooms pitcher et al 1995 pitcher and boyd 1996 red tide has therefore been closely related to the prevailing winds of the region which govern most hydrodynamic processes on the continental shelf pitcher et al 1998 these observations are considered to reflect the consequences of two important influences of the surface boundary layer on the development of red tide the dynamics of the upper mixed layer in determining species selection and development and the role of mesoscale circulation in bloom retention and advection in the southern benguela three upwelling centers may be distinguished all of which coincide with a narrowing of the shelf the namaqua 30us cape columbine 33us and cape peninsula 34us upwelling centers fig 1 the region to the north of the cape columbine cell is particularly susceptible to red tide formation and its negative impacts and a historical perspective of faunal mortalities associated with red tides in this region is given by cockcroft et al 2000 here topographic and bathymetric features alter current patterns and mixing regimes features considered important in the development of red tide the shelf broadens to the north of columbine favoring stratification and stability of the water column airborne radiometer studies within this region have identified upwelling off cape columbine and along the coast north of dwarskersbos jury 1985 taunton clark 1985 under conditions of upwelling an equatorward coastal jet is formed off the columbine headland but wind stress shear promotes clockwise circulation within st helena bay jury 1985 thereby favoring retentive nearsurface circulation patterns within the region holden 1985 penven et al 2000 alongshore variability of flow considered to play a dominant role in driving the southward advection of phytoplankton blooms is thought to be associated with barotropic flow inshore generated by coastally trapped waves over the southern namaqua shelf with periods of 3 to 6 d lamberth and nelson 1987

sediment sound velocities from sonobuoys sunda trench and forearc basins nicobar and central bengal fans and andaman sea basins supplement is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington dc 20009 document b83 007 2 50 payment must accompany order measurements of mean sound velocities in the first largely unlithified layers in the seafloor were made using the sonobuoy technique in several areas in the northern indian ocean older measurements were added to new measurements and regressions for mean and instantaneous velocity versus one way travel time of sound are presented for the central bengal fan the central andaman sea basin the nicobar fan and the sunda trench new data and regression equations are presented for the mergui north sumatra basin and for four forearc basins between sumatra and java and the sunda trench minimum velocity gradients were found in those areas where sedimentation rates were high and sediments have accumulated in thick sections which have not had time to fully consolidate porosity in the top of the sediment section has not been fully reduced under overburden pressure these minimum velocity gradients just under the seafloor were found in the four forearc basins where they ranged from 0 34 s 1 to 0 84 s 1 with an average of 0 58 s 1 the near surface velocity gradient in the sunda trench was 1 33 s 1 but was higher in the adjacent fossil nicobar fan 1 62 s 1 in the surface of the bengal fan the velocity gradient was low in the upper fan 0 86 s 1 high in the central fan 1 94 s 1 and again lower in the southern fan 1 18 s 1 which may support sedimentation models calling for bypassing of the central fan and higher rates of accumulation on the southern fan

abundance major element composition and size of components and matrix in cv co and acfer 094 chondrites abstract the relative abundances and chemical compositions of the macroscopic components or inclusions chondrules and refractory inclusions and fine grained mineral matrix in chondritic meteorites provide constraints on astrophysical theories of inclusion formation and chondrite accretion we present new techniques for analysis of low count pixel si mg ca al ti and fe x ray intensity maps of rock sections and apply them to large areas of co and cv chondrites and the ungrouped acfer 094 chondrite for many thousands of manually segmented and type identified inclusions we are able to assess pixel by pixel the major element content of each inclusion we quantify the total fraction of refractory elements accounted for by various types of inclusion and matrix among co chondrites both matrix and inclusion mg si ratios approach the solar and bulk co ratio with increasing petrologic grade but si remains enriched in inclusions relative to matrix the oxidized cv chondrites with higher matrix inclusion ratios exhibit more severe aqueous alteration oxidation and their excess matrix accounts for their higher porosity relative to reduced cv chondrites porosity could accommodate an original ice component of matrix as the direct cause of local alteration of oxidized cv chondrites we confirm that major element abundances among inclusions differ greatly across a wide range of co and cv chondrites these abundances in all cases add up to near chondritic solar bulk abundance ratios in these chondrites despite wide variations in matrix inclusion ratios and inclusion sizes chondrite components are complementary this complementarity provides a robust meteoritic constraint for astrophysical disk models

origin of low ca pyroxene in amoeboid olivine aggregates evidence from oxygen isotopic compositions amoeboid olivine aggregates aoas in primitive carbonaceous chondrites consist of forsterite fa 50 objects is texturally and mineralogically intermediate between aoas and al rich chondrules it consists of euhedral forsterite grains pigeonite augite anorthitic mesostasis abundant anhedral spinel grains and minor fe ni metal it is surrounded by a coarse grained igneous rim largely composed of low ca pyroxene with abundant fe ni metal sulfide nodules the mineralogical observations suggest that only spinel grains in this igneous object were not melted the spinel is 16o rich 17o 22 whereas the neighboring plagioclase mesostasis is 16o depleted 17o 11 we conclude that aoas are aggregates of solar nebular condensates forsterite fe ni metal and cais composed of al diopside anorthite spinel and melilite formed in an 16o rich gaseous reservoir probably cai forming region s solid or incipiently melted forsterite in some aoas reacted with gaseous sio in the same nebular region to form low ca pyroxene some other aoas appear to have accreted 16o poor pyroxene normative dust and experienced varying degrees of melting most likely in chondrule forming region s the most extensively melted aoas experienced oxygen isotope exchange with 16o poor nebular gas and may have been transformed into chondrules the original 16o rich signature of the precursor materials of such chondrules is preserved only in incompletely melted grains

nanometer scale mineralogy and petrography of fine grained aggregates in anhydrous interplanetary dust particles abstract fine grained matrices in seven solar flare track rich anhydrous interplanetary dust particles idps were studied using 200 kev analytical electron microscopy the idps are u222b42 u220a19 u222b28 u230a3 w7027a11 w7027h14 u219 c2 and u219 c11 the matrices are composed of aggregates of glass disordered carbonaceous material and crystalline mineral grains with diameters between 1 and 150 nm the mineral grains were characterized using lattice fringe imaging electron microdiffraction and quantitative energy dispersive x ray spectroscopy eds the glasses were studied using eds and electron energy loss near edge structure analysis elnes three types of aggregates were observed unequilibrated equilibrated and reduced aggregates unequilibrated aggregates uas are 0 1 0 3 m diameter objects with bulk major element compositions that are approximately chondritic solar except for carbon they contain feni metal and fe rich sulfide crystals between 1 and 20 nm diameter embedded in silicate glass equilibrated aggregates eas are 0 1 to 1 m diameter objects that exhibit melt textures and mineralogy they contain fe bearing olivine and pyroxene grains with equilibrated fe mg ratios and fe sulfides embedded in feldspathic alumino silicate glass reduced aggregates ras are 0 1 to 1 0 m objects with feni metal feni carbides and fe rich sulfides embedded in a carbonaceous matrix the aggregates in the seven anhydrous idps appear to have formed in diverse physiochemical environments

matrices of type 3 ordinary chondrites primitive nebular records petrologic studies were made on the fine grained matrices of type 3 ordinary chondrites of the lowest petrologic subtype the matrix minerals in order of abundance are olivine fo99 to fo9 enstatite or bronzite augite or subcalcic augite albite fe ni metal troilite magnetite spinel mgal2o4 chromite and calcite fe and mg rich fluffy particles and albite like particles are also major constituents the chemical compositions of olivine and pyroxenes vary within and among the chondrites and are in gross disequilibrium showing that the matrix materials were hardly heated after their formation textural relationships indicate that magnesian olivine was formed after ca pyroxene followed by intermediate to iron rich olivine intermediate olivine was formed from enstatite and metallic iron under relatively oxidizing conditions the observations indicate that matrices of chondrites are neither the fragments of chondrules nor the precursors of chondrules they were mostly the products of condensation and reaction among solids and or between solids and the ambient gas mostly at low temperatures and thus they contain records of primitive processes in the nebula in order to explain the presence of olivines more iron rich than fo50 the presence of free sio2 or a high activity of sio2 in the gas is necessary which was not shown in previous thermochemical calculations mineral assemblages of matrix minerals of chondrites of different chemical groups differ systematically according to oxidation state of the parental meteorites indicating that they were formed at different oxygen fugacities the rims of chondrules and surrounding matrix materials must have accreted onto chondrules during turbulent movements of the nebula

evidence for aqueous alteration in a carbonaceous xenolith from the plainview h5 chondrite abstract within a cm like clast in the plainview h5 chondrite are two inclusions which have the distinctive morphologies of an allende like coarse grained cai and an amoeboid olivine inclusion respectively the compositions of the mineral components within the inclusions were ascertained in this microprobe study the major constituents of the altered inclusions are calcite mg fe rich phyllosilicates fe ti oxides and an unusually al rich 21 32 wt a1 2 o 3 phyllosilicate assuming the starting compositions for these inclusions suggested by their morphologies namely ca al refractory rich oxides and silicates the alteration process would have required transport of na cl h 2 o co 2 and feo because significant quantities of iron are required to produce the mineral assemblages now present from the inferred starting materials and because of the presence of hydrous phases it seems that liquid water was probably the medium in which the alteration reactions took place the two possible sources of liquid water in meteorite parent bodies are primordially formed clay minerals and water ice as yet neither source can be ruled out

seasonal cycle of n p ta stoichiometry as a modulator of co2 buffering in eastern boundary upwelling systems 1 in this study we use the southern benguela upwelling system to investigate the role of nutrient and carbon stoichiometry on carbonate dynamics in eastern boundary upwelling systems six months in 2010 were sampled along a cross shelf transect data were classified into summer autumn and winter nitrate phosphate dissolved inorganic carbon and total alkalinity ratios were used in a stoichiometric reconstruction model to determine the contribution of biogeochemical processes on a parcel of water as it upwelled deviations from the redfield ratio were dominated by denitrification and sulfate reduction in the subsurface waters the n p ratio was lowest 7 2 during autumn once anoxic waters had formed total alkalinity ta generation by anaerobic remineralization decreased pco2 by 227 atm ventilation during summer and winter resulted in elevated n p ratios 12 3 we propose that anaerobic production of ta has an important regional effect in mitigating naturally high co2 and making upwelled waters less corrosive citation gregor l and p m s monteiro 2013 seasonal cycle of n p ta stoichiometry as a modulator of co2 buffering in eastern boundary upwelling systems geophys res lett 40 doi 10 1002 2013gl058036

alteration of al rich inclusions inside amoeboid olivine aggregates in the allende meteorite lightly altered al rich inclusions in amoeboid olivine aggregates have cores containing primary melilite fassaite spinel perovskite and no secondary alteration products in moderately altered inclusions whose cores now contain only fassaite spinel perovskite melilite was replaced by a fine grained mixture of grossular anorthite feldspathoids and perovskite was partially replaced by ilmenite in heavily altered inclusions fassaite has been replaced by a mixture of phyllosilicates ilmenite and the remaining primary phases are spinel perovskite in very heavily altered inclusions no primary phases remain the spinel having reacted to form either phyllosilicates or a mixture of olivine feldspathoids this sequence of alteration reactions may reflect successively lower solar nebular equilibration temperatures during alteration sio2 na2o k2o feo cr2o3 h2o and cl were introduced into the inclusions and cao was lost mgo may have been lost during the melilite reaction and added during formation of phyllosilicates electron microprobe analyses indicate that the phyllosilicates are a mixture of na rich phlogopite and chlorite or alrich serpentine thermodynamic calculations suggest that at a solar nebular water fugacity of 10 6 na rich phlogopite could have formed from fassaite at 470 k and chlorite from na rich phlogopite at 328 k olivine mantling al rich inclusions is not serpentinized suggesting that these objects stopped equilibrating with the nebular gas above 274 k

fayalite in the kaba and mokoia carbonaceous chondrites abstract the olivines in the kaba and mokoia cv3 carbonaceous chondrites range from almost pure forsterite fo99 6 to almost pure fayalite fa99 9 individual grains of fayalite of such high purity have not previously been reported from meteorites they can reach 100 m in diameter and occur in the matrix chondrules forsterite enstatite aggregates and rims around ca al rich inclusions chondrules and aggregates the fayalite is three to nine times richer in mn than in bulk ci chondrites many grains are associated with magnetite troilite and pentlandite an assemblage that suggests relatively oxidizing conditions we propose that the fayalite formed through reaction of sio g released by decomposition of enstatite with magnetite and sulfide the lower thermal limit for fayalite formation is determined by the above reaction whereas the upper thermal limit is controlled by magnetite stability thermodynamic calculations indicate that fayalite coexisting with magnetite and sulfides could have formed in a nebular environment that had a h 2 o h 2 ratio substantially greater than the canonical solar nebula coexisting olivines having endmember compositions indicate that they experienced little or no thermal metamorphism

oxygen isotope heterogeneity in chondrules from the mokoia cv3 carbonaceous chondrite we report a study of the oxygen isotope ratios of chondrules and their constituent mineral grains from the mokoia oxidized cv3 chondrite bulk oxygen isotope ratios of 23 individual chondrules were determined by laser ablation fluorination and oxygen isotope ratios of individual grains mostly olivine were obtained in situ on polished mounts using secondary ion mass spectrometry sims our results can be compared with data obtained previously for the oxidized cv3 chondrite allende bulk oxygen isotope ratios of mokoia chondrules form an array on an oxygen three isotope plot that is subparallel to and slightly displaced from the ccam carbonaceous chondrite anhydrous minerals line the best fit line for all cv3 chondrite chondrules has a slope of 0 99 and is displaced significantly by 17o 2 5 from the young and russell slope one line for unaltered calcium aluminum rich inclusion cai minerals oxygen isotope ratios of many bulk cais also lie on the cv chondrule line which is the most relevant oxygen isotope array for most cv chondrite components bulk oxygen isotope ratios of most chondrules in mokoia have 18o values around 0 and olivine grains in these chondrules have similar oxygen isotope ratios to their bulk values in general it appears that chondrule mesostases have higher 18o values than olivines in the same chondrules our bulk chondrule data spread to lower 18o values than any ferromagnesian chondrules that have been measured previously two chondrules with the lowest bulk 18o values 7 5 and 11 7 contain olivine grains that display an extremely wide range of oxygen isotope ratios down to 17o 18o around 50 in one chondrule in these chondrules there are no apparent relict grains and essentially no relationships between olivine compositions which are homogeneous and oxygen isotopic compositions of individual grains heterogeneity of oxygen isotope ratios within these chondrules may be the result of incorporation of relict grains from objects such as amoeboid olivine aggregates followed by solid state chemical diffusion without concomitant oxygen equilibration alternatively oxygen isotope exchange between an 16o rich precursor and an 16o poor gas may have taken place during chondrule formation and these chondrules may represent partially equilibrated systems in which isotopic heterogeneities became frozen into the crystallizing olivine grains if this is the case we can infer that the earliest nebular solids from which chondrules formed had 17o and 18o values around 50 similar to those observed in refractory inclusions

crystallization sequences of ca al rich inclusions from allende an experimental study the equilibrium crystallization sequence at 1 atmosphere in air of a melt corresponding in composition to the average composition of type b ca al rich inclusions from the allende meteorite is spinel 1550 c melilite 1400 c ak22 anorthite 1260 c ti al rich clinopyroxene 1230 c ti fassaite the melilite becomes increasingly akermanitic with decreasing temperature the pyroxene is similar in composition to fassaites from type b inclusions preliminary results suggest that the crystallization sequence is similar at oxygen fugacities near the iron wustite buffer the results of these experiments have been integrated with available phase equilibrium data in the system cao mgo al 2o 3 sio 2tio 2 and a phase diagram for predicting the crystallization sequences of liquids with compositions of coarse grained ca al rich inclusions has been developed available bulk compositions of coarse grained inclusions form a well defined trend in terms of major elements extending from type a and bl inclusions near the spinel melilite join to more pyroxene rich type b2 inclusions the trend deviates from the expected sequence of solid condensates from a nebular gas at p 10 3 atm if pure diopside is assumed to be the clinopyroxene that condenses the type a b1 end of the trend is similar in composition to calculated equilibrium condensates at 1202 1227 c and the trend as a whole parallels the sequence of condensates expected from diopside condensation at 1170 c the trend is consistent to first order with the condensation of solid ti rich fassaite in place of pure diopside at higher temperatures than those at which pure diopside is predicted to condense partially molten condensates may be likely in this case or if the nebular pressure is higher than 10 3 atm

dark inclusions in the mokoia cv3 chondrite evidence for aqueous alteration and subsequent thermal and shock metamorphism mokoia is a cv3 chondrite that contains abundant phyllosilicate mineralization we present a detailed petrographic and scanning electron microscopic study of 24 dark inclusions dis that we found in mokoia the overall texture and constituent minerals of the dis resemble those in the host meteorite fe bearing saponite and na rich phlogopite the same phyllosilicates as in the host meteorite occur in the dis which strongly suggests that the dis have a similar alteration history to the host meteorite however the dis show several distinct differences from the host meteorite olivine grains in the di matrices are more homogeneous in fe fe mg ratio than those in the host meteorite matrix phyllosilicates in the dis are less abundant than in the host meteorite and they have been dehydrated to various extents these characteristics suggest that the dis have experienced higher degree of thermal metamorphism than the host meteorite in addition the matrices in the dis are more compacted than those in the host meteorite most olivine grains in the dis show undulatory extinction in transmitted crossed polarized light and some show planar fractures while such olivine grains are rare in the host meteorite two of the dis contain si mg fe and o rich melt veins these characteristics indicate that most dis have been shocked to shock stage s3 s4 while the host meteorite is shock stage s1 virtually unshocked thermal metamorphism of the dis was likely caused by shock heating these results are consistent with the contention previously proposed for the dis in cv3 chondrites i e the dis have experienced aqueous alteration and subsequent dehydration on the cv parent body we suggest that thermal and shock metamorphism occurred locally to various extents after pervasive aqueous alteration in the mokoia parent body

fayalitic halos around inclusions in forsterites from carbonaceous chondrites abstract spindle shaped fayalitic halos occur in forsterites of the allende kaba mokoia vigarano and ningqiang carbonaceous chondrites the halos have 1 ellipsoidal or less commonly rounded shapes 2 long axes parallel to each other within given host crystals 3 round bleb like inclusions of ni rich metal and sulfide in their centers and 4 compositional gradients that are most fe rich near the inclusions the fe and mg compositional profiles are well approximated by the error function which in combination with halo shapes indicates a diffusional origin the high ni contents relative to kamacite of the metal inclusions suggest fe loss we propose that the halos formed by oxidation of the fe ni metal in the inclusions and fe 2 diffusion into adjoining forsterite the halo dimensions suggest they formed between 1000 and 1250 k carbonaceous chondrites are characterized by among other features minerals and some organic molecules that are only stable at relatively low temperatures probably less than 500 k and certainly lower than 800 k the conditions required to form the fayalitic halos by diffusion are inconsistent with such low temperatures this combination leads us to conclude that the halos formed prior to their incorporation in the parent body ies of their host meteorites possibilities are that the halos formed in the nebula or within a prior parent body from which material was dispersed and reaggregated

amoeboid olivine aggregates with low ca pyroxenes a genetic link between refractory inclusions and chondrules amoeboid olivine aggregates aoas in primitive unmetamorphosed and unaltered carbona ceous chondrites are uniformly 16 o enriched 17 o 20 and consist of forsterite fa2 feni metal and a refractory component individual cais and fine grained minerals interspersed with forsterite grains composed of al diopside anorthite spinel and exceptionally rare melilite a u k15 some cais in aoas have compact igneous textures melilite in aoas is replaced by a fine grained mixture of spinel al diopside and anorthite spinel is corroded by anorthite or by al diopside in 10 of 500 aoas studied in the cr cv cm co ch cb and ungrouped carbonaceous chondrites acfer 094 adelaide and lew85332 forsterite is replaced to a various degree by low ca pyroxene there are three major textural occurrences of low ca pyroxene in aoas i thin 10 m discontinuous layers around forsterite grains or along forsterite grain boundaries in aoa peripheries ii haloes and subhedral grains around feni metal nodules in aoa peripheries and iii thick up to 70 m continuous layers with abundant tiny inclusions of feni metal grains around aoas aoas with low ca pyroxene appear to have experienced melting of various degrees in the most extensively melted aoa in the cv chondrite leoville only spinel grains are relict forsterite anorthite and al diopside were melted this aoa has an igneous rim of low ca pyroxene with abundant feni metal nodules and is texturally similar to type i chondrules based on these observations and thermodynamic analysis we conclude that aoas are aggregates of relatively low temperature solar nebular condensates originated in 16 o rich gaseous reservoir s probably cai forming region s some of the cais were melted before aggregation into aoas many aoas must have also experienced melting but of a much smaller degree than chondrules before and possibly after aggregation melilite and spinel reacted with the gaseous sio and mg to form ca tschermakite caal2sio6 diopside camgsi2o6 solid solution and anorthite solid or incipiently melted olivine in some aoas reacted with gaseous sio in the cai or chondrule forming regions to form low ca pyroxene mg2sio4 sio g h2o g mg2si2o6 h2 g some low ca pyroxenes in aoas may have formed by oxidation of si bearing feni metal mg2sio4 si in feni 2h2o g mg2si2o6 2h2 g and by direct gas solid condensation mg g sio g h2o g mg2si2o6 s h2 g from fractionated mg si ratio solar nebular gas although bulk compositions of aoas are rather similar to those of type i chondrules on the projection from spinel onto the plane ca2sio4 mg2sio4 al2o3 these objects plot on different sides of the anorthite forsterite thermal divide suggesting that type i chondrules cannot be produced from aoas by an igneous fractionation formation of low ca pyroxene by reaction of aoas with gaseous sio and by melting of silica rich dust accreted around aoas moves bulk compositions of the aoas towards chondrules and provide possible mechanisms of transformation of refractory materials into chondrules or chondrule precursors the rare occurrences of low ca pyroxene in aoas may indicate that either aoas were isolated from the hot nebular gas before condensation of low ca pyroxene or that condensation of low ca pyroxene by reaction between forsterite and gaseous sio was kinetically inhibited if the latter is correct then the common occurrences of pyroxene rich type i chondrules may require either direct condensation of low ca pyroxenes or sio2 from fractionated nebular gas or condensation of gaseous sio into chondrule melts copyright 2004 elsevier ltd

a refractory inclusion in the kaba cv3 chondrite some implications for the origin of spinel rich objects in chondrites abstract the first detailed petrographic and mineralogical study of a ca al rich inclusion cai from the kaba cv3 chondrite is reported this fine grained cai contains abundant small rounded rimmed spinel rich objects which have important features in common with the spinel rich objects in other carbonaceous and ordinary chondrites these nodules are interpreted as fractionated distillation residues of primitive dust however the available data do not unambiguously rule out a condensation origin for at least some of these objects finally the preservation of distinct diopside hedenbergite rims on the spinel rich bodies and the small grain size of many minerals in the cai matrix material both suggest that the cai accreted cool and had a relatively cool thermal history in the kaba parent body

refractory residues condensates and chondrules from solar furnace experiments vertical access solar furnace experiments have produced refractory residues condensates and chondrules that are similar to components of chondritic meteorites in particular ca al rich refractory residues similar in chemistry to inclusions in carbonaceous chondrites have been produced by partial evaporation of basaltic bulk rock samples fe mg si rich condensates with distinctive microbotryoidal morphology have been collected from the same sample runs particle coatings and aggregates with virtually identical microbotryoidal morphology and major element chemistry have been identified in both the allende and murchison meteorites spattered drops from melt beads undergoing heating and partial evaporation resemble some meteoritic chondrules in their mineralogies textures grain size and sorting the spatter mechanism is highly efficient in the production of chondrules if any of the refractory inclusions in chondrites are in fact partial evaporation residues many meteoritic fluid drop chondrules must have been formed by this process the hot central portion of the solar nebula acting on a cloud of dust and gas is the probable source of heat required to produce the fractionated chemistry and physical state of many of the components of chondritic meteorites

mineral chemistry and origin of spinel rich inclusions in the allende cv3 chondrite the mineral chemistry of 20 spinel rich inclusions and spinel rich nodules in 16 olivine rich inclusions in allende was studied by electron probe microanalysis variations in the chemistry of hibonite are explained by a coupled substitution among al ti mg si fe and v two types of perovskite occur 1 1 a variety enriched in the super refractory trace elements zr and y 2 2 zr y poor perovskite spinel typically contains a significant amount of fe 5 wt feo and small amounts of cr v zn ca and ti there are positive crfe and znfe correlations in fe rich spinel mg rich clinopyroxenes that rim spinel generally contain 11 wt a12o3 3 wt tio2 and 2 wt feo the chemistry of many accessory minerals in the inclusions was also studied the mineralogy of spinel rich allende inclusions is similar to the mineralogy of fine grained ca al rich inclusions cai s in alh 77003 and rims on coarse grained cai s in allende spinel rich inclusions in mokoia kaba and murchison differ in that they contain fe poor spinel and lack feldspathoid rims the mineralogy mineral chemistry and bulk chemistry of spinel rich allende inclusions indicate that they are not primitive aggregates of crystalline nebular condensates the inclusions are aggregates of tiny concentric objects each of which we interpret to be a fractionated distillation residue that lost ca si rich partial melt we believe that the mineral chemistry of spinel rich allende inclusions rims on coarse grained cai s and olivine rich allende inclusions and chondrules was largely established in the solar nebula at high temperatures under moderately oxidizing conditions and later modified to some degree by mild thermal metamorphism in the allende parent body we suggest that interstellar dust aggregates were melted or distilled into allende inclusions by aerodynamic drag heating in regions of the nebula where the dust gas ratio was so enhanced that the local oxygen fugacity was raised by several orders of magnitude and liquids became thermodynamically stable

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

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

aqueous alteration in the kaba cv3 carbonaceous chondrite the kaba cv3 carbonaceous chondrite has undergone pervasive aqueous alteration that produced fe bearing saponite in chondrules and matrix saponite in chondrules is coarse grained and shows a crystallographic orientation relationship such that c of saponite parallels a of enstatite matrix saponite exhibits a variety of textures including coarse and fine grained clusters isolated packets and sparse lamellar replacements of fe rich olivine the coarse grained clusters were probably derived from altered chondrules that were fragmented during regolith gardening the fine grained clusters and isolated packets formed from material released during the partial dissolution of matrix silicates much saponite is associated with submicron fe ni sulfides suggesting that conditions were not oxidizing during aqueous alteration we believe that the alteration occurred after accretion and on the kaba parent body because saponite is present throughout the sample by analogy to terrestrial occurrences the saponite in kaba probably formed at low temperatures 100 c the distribution of saponite in kaba is determined by local bulk compositions enstatite in chondrules has been altered more extensively than the fine grained olivine in matrix the alteration products in kaba resemble those in other aqueously altered carbonaceous chondrites such as the mokoia cv3 chondrite and in certain ci chondrites there are however significant differences kaba lacks the abundant high al phyllosilicates in chondrules and in cais reported from mokoia also lacking in kaba is the serpentine and ferrihydrite found in orgueil alteration products in kaba matrix are dissimilar from those in co3 chondrites even though their prealteration mineralogies were similar an observation that probably reflects different temperatures during alteration

ca al rich inclusions in rumuruti r chondrites rumuruti chondrites r chondrites constitute a well characterized chondrite group different from carbonaceous ordinary and enstatite chondrites many of these meteorites are breccias containing primitive type 3 fragments as well as fragments of higher petrologic type ca al rich inclusions cais occur within all lithologies here we present the results of our search for and analysis of al rich objects in rumuruti chondrites we studied 20 r chondrites and found 126 ca al rich objects 101 cais 19 al rich chondrules and 6 spinel rich fragments based on mineralogical characterization and analysis by sem and electron microprobe the inclusions can be grouped into six different types 1 simple concentric spinel rich inclusions 42 2 fassaite rich spherules 3 complex spinel rich cais 53 4 complex diopside rich inclusions 5 al rich chondrules and 6 al rich spinel rich fragments the simple concentric and complex spinel rich cais have abundant spinel and based on the presence or absence of different major phases fassaite hibonite na al cl rich alteration products can be subdivided into several subgroups although there are some similarities between cais from r chondrites and inclusions from other chondrite groups with respect to their mineral assemblages abundance and size the overall assemblage of cais is distinct to the r chondrite group some ca al rich inclusions appear to be primitive e g low feo contents in spinel low abundances of na al cl rich alteration products abundant perovskite whereas others were highly altered by nebular and or parent body processes e g high concentrations of feo and zno in spinel ilmenite instead of perovskite abundant na al cl rich alteration products there is complete absence of grossite and melilite which are common in cais from most other groups cais from equilibrated r chondrite lithologies have abundant secondary ab rich plagioclase oligoclase and differ from those in unequilibrated type 3 lithologies which have nepheline and sodalite instead

lime silicates in amoeboid olivine aggregates in carbonaceous chondrites indicator of nebular and asteroidal processes mno feo ratios in olivine from amoeboid olivine aggregates aoas reflect conditions of nebular condensation and can be used in concert with matrix textures to compare metamorphic conditions in carbonaceous chondrites lime low iron mn enriched olivine was identified in aoas from y 81020 co3 05 kaba cv 3 1 and in y 86009 cv3 y 86751 cv3 nwa 1152 cr cv3 but was not identified in aoas from efremovka cv3 1 3 4 or allende cv 3 6 according to thermodynamic models of nebular condensation lime olivine is stable at lower temperatures than mn poor olivine and at low oxygen fugacities dust enrichment 95 in our study whereas efremovka aoas are slightly fe rich fo 92 aoa olivines from kaba are mostly forsteritic but rare fe rich olivine precipitated from an aqueous fluid a combination of precipitation of fe rich olivine and diffusion of fe into primary olivine grains resulted in iron rich compositions fo97 59 in allende aoas variations from fine grained nonporous matrix toward higher porosity and coarser lath like matrix olivine can be divided into six stages represented by 1 y 81020 efremovka nwa 1152 2 y 86751 lithology b 3 y 86009 4 kaba 5 y 86751 lithology a 6 allende these stages are inferred to represent general degree of metamorphism although the specific roles of thermally driven grain growth and diffusion versus aqueous dissolution and precipitation remain uncertain

hydrous and anhydrous alterations of chondrules in kaba and mokoia cv chondrites chondrules in the bali like cv chondrite kaba and the allende like portion of the mokoia breccia have been studied to explore the relationship between hydrous alteration to form phyllosilicates and anhydrous alteration resulting in secondary olivine zonation replacement of enstatite by ferroan olivine and formation of feldspathoids nepheline and sodalite all kaba chondrules experienced extensive hydrous alteration whereas anhydrous alteration was minor and resulted only in the olivine zonation on the other hand all of the mokoia chondrules experienced both extensive anhydrous and hydrous alteration bronzite rims formed between relic enstatite grains and phyllosilicates in both kaba and mokoia during the hydrous alteration petrographic observations indicate that phyllosilicates in mokoia postdate formation of the secondary ferroan olivine and feldspathoids we conclude that anhydrous alteration in kaba and mokoia predated hydrous alteration and took place before accretion of chondrules into the cv parent asteroid

connection between micrometeorites and wild 2 particles from antarctic snow to cometary ices we discuss the relationship between large cosmic dust that represents the main source of extraterrestrial matter presently accreted by the earth and samples from comet 81p wild 2 returned by the stardust mission in january 2006 prior examinations of the stardust samples have shown that wild 2 cometary dust particles contain a large diversity of components formed at various heliocentric distances these analyses suggest large scale radial mixing mechanism s in the early solar nebula and the existence of a continuum between primitive asteroidal and cometary matter the recent collection of concordia antarctic micrometeorites recovered from ultra clean snow close to dome c provides the most unbiased collection of large cosmic dust available for analyses in the laboratory many similarities can be found between antarctic micrometeorites and wild 2 samples in terms of chemical mineralogical and isotopic compositions and in the structure and composition of their carbonaceous matter cosmic dust in the form of concordia antarctic micrometeorites and primitive idps are preferred samples to study the asteroid comet continuum

laboratory simulation of the physical processes occurring on and near the surfaces of comet nuclei laboratory comet simulation experiments are discussed in the context of theoretical models and recent ground based and spacecraft observations especially the giotto observations of p halley the set up of various comet simulation experiments is reviewed a number of small scale experiments have been performed in many laboratories since the early 1960s however the largest and most ambitious series of experiments were the comet simulation experiments known as kosi german kometen simulation these experiments were prompted by the appearance of comet p halley in 1986 and in planning for the european space agency s rossetta mission that was originally scheduled to return samples they were performed between 1987 and 1993 using the german space agency s dlr space hardware testing facilities in cologne as with attempts to reproduce any natural phenomenon in the laboratory there are deficiencies in such experiments while there are major new insights to be gained simulation experiments have enabled the development of methods for making comet analogues and for exploring the properties of such materials in detail these experiments have provided new insights into the morphology and physical behavior of aggregates formed from silicate grains likely to exist in comets formation of a dust mantle on the surfaces and a system of ice layers below the mantle caused by chemical differentiation have been identified after the insolation of the artificial comet the mechanisms for heat transfer between the comet s surface and its interior the associated gas diffusion from the interior of the surface and compositional structural and isotopic changes that occur near the surface have been described by modeling the experimental results the mechanisms of the ejection of dust and ice grains from the surface and the importance of gas drag in propelling grains have also been explored

petrology of types 4 6 carbonaceous chondrites we have studied the petrology of three type 4 carbonaceous chondrites coolidge karoonda and pecora escarpment 82500 which was previously classified as an ll6 chondrite and compared them to published descriptions of the other known metamorphosed c chondrites yamato 6903 and mulga west all except coolidge have abundant matrix typically 80 vol composed largely of homogeneous olivine fa 29 33 and surprisingly heterogeneous plagioclase mostly an 20 75 their opaque mineralogy indicates high oxygen fugacities during metamorphism metallic fe ni and troilite are rare and magnetite and pentlandite are abundant with accessory pyrrhotite chalcopyrite and pyrite possibly because of a lower matrix abundance coolidge has more reduced minerals metallic fe ni and olivine with fa 14 the properties of all c4 6 chondrites appear to be consistent with an origin by metamorphism of c3 like precursors by processes analogous to those operating in ordinary chondrite parent bodies or planetesimals however type 4 6 material was not well mixed with type 3 material in the cv3 parent body as it was in the ordinary chondrite parent bodies conceivably c4 6 chondrites come from one or more separate parent bodies

secondary calcium iron rich minerals in the bali like and allende like oxidized cv3 chondrites and allende dark inclusions we have characterized ca fe rich silicates salite hedenbergite pyroxenes fs10 50wo45 50 andradite ca3fe2si3o12 kirschsteinite cafesio4 and wollastonite ca3si3o9 in the type i chondrules and matrices in the bali like and allende like oxidized cv3 chondrites and allende dark inclusions in type i chondrules in the bali like cv3 chondrites metal is oxidized to magnetite magnetite sulfide nodules are replaced by ca fe rich pyroxenes with minor andradite and pure fayalite we infer that ca fe rich pyroxenes andradite fayalite magnetite and phyllosilicates which occur in mesostases formed at relatively low temperatures 300 c in the presence of aqueous solutions thermodynamic analysis of phase relations in the si fe ca o h system and large o isotopic fractionation of the coexisting magnetite and fayalite 20 krot et al 1998 are consistent with this interpretation in type i chondrules in the allende like cv3 chondrites and dark inclusions magnetite sulfide nodules are replaced by ca fe rich pyroxenes and ferrous olivine low ca pyroxene and forsterite phenocrysts are rimmed and veined by ferrous olivine it appear that the ca fe rich pyroxenes predate formation of ferrous olivine the latter postdates formation of talc and biopyriboles brearley 1997 the allende dark inclusions are crosscut by ca fe pyroxene andradite veins and surrounded by ca rich rims that consist of ca fe rich pyroxenes andradite wollastonite and kirschsteinite calcium rich veins and rims formed after aggregation and lithification of the dark inclusions the rimmed dark inclusions show zoned depletion in ca which is due to a lower abundance of ca fe rich pyroxenes close to the rim calcium was probably leached from the inclusions and redeposited along their edges we infer that the allende like chondrites and dark inclusions experienced similar aqueous alteration to the bali like chondrites and were metamorphosed subsequently which resulted in loss of aqueous solutions and dehydration of phyllosilicates we conclude that ca fe rich silicates in the oxidized cv3 chondrites and allende dark inclusions are secondary and resulted from aqueous fluid rock interactions during progressive metamorphism of a heterogeneous mixture of hydrous ices and anhydrous materials the latter were possibly mineralogically similar to the reduced cv3 chondrites

domain wall dynamics in 4c pyrrhotite at low temperature summary monoclinic 4c pyrrhotite fe7s8 is ferrimagnetic due to an ordered defect structure with alternating vacancy and vacancy free sublattices its low temperature magnetic transition near 35k is characterized by the distinct increase in coercivity and remanent magnetization the increase of these parameters has been attributed to changes in the domain wall structure we present static and dynamic magnetization data of a powder sample to study the domain wall dynamics across the low temperature transition the amplitude dependent ac susceptibility and the ferromagnetic resonance spectroscopy indicate that the hardening of the domain wall pinning at the transition occurs simultaneously with the decrease in initial saturation remanent magnetization these two effects are explained by the enhanced inhomogeneity of the bulk material caused by the persistency of the ordered vacancies and by newly formed defects due to localized distortion of fe ii sites in the vacancy free sublattice the generated localized defects are the link between the domain wall dynamics and the low temperature transition in 4c pyrrhotite

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

petrography and classification of ca al rich and olivine rich inclusions in the allende cv3 chondrite a detailed systematic petrographic survey of all 189 ca al rich and olivine rich inclusions larger than 0 2 mm in diameter in 17 thin sections of allende was performed by optical and scanning electron microscopy most of these inclusions are aggregates containing varying proportions of three distinct constituents termed concentric objects chaotic material and inclusion matrix a new classification system for allende inclusions is proposed olivine rich inclusions occur in two textural varieties unrimmed olivine aggregates type 1a inclusions and rimmed olivine aggregates type 1b inclusions we classify ca al rich inclusions cai s on the basis of the size and abundance of their constituent concentric objects rather than their grain size into unrimmed complex cai s type 2 inclusions rimmed complex cai s type 3 inclusions and simple cai s type 4 inclusions several of the inclusion classes grade into each other some fundamental relationships among various types of allende inclusions are discussed we suggest that the term coarse grained even if used only in a relative sense is too restrictive for some members of one class of inclusion simple cai s and is inappropriate for most members of another class melilite rich complex cai s

an asteroidal breccia the anatomy of a cluster idp abstract we report results of a consortium study of a large interplanetary dust particle known as cluster l2008 5 this cluster is composed of fifty three fragments 5 pm in diameter and several hundred fines several methods were used to estimate the degree of heating that this cluster experienced variations in the inferred peak temperatures experienced by different fragments suggest that a thermal gradient was maintained the cluster as a whole was not strongly heated it is estimated to have a low earth encounter velocity which is consistent with origin from an object in an asteroidal orbit rather than from a comet which would most likely have a high entry velocity our conclusions show that cluster l2008 5 consists of a chemically and mineralogically diverse mixture of fragments we believe that cluster l2008 5 represents a heterogeneous breccia and that it was most likely derived from an object in an asteroidal orbit we also present an important cautionary note for attempts to interpret individual small sized 10 15 m idps as representative of parent bodies it is not unique that individual building blocks of idps such as discrete olivine pyroxene sulfide grains regions of carbonaceous material and other noncrystalline material are found in several fragments however it is unique that these building blocks are combined in various proportions in related idps from one large cluster particle