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

the origin of ferrous zoning in allende chondrule olivines abstract olivine crystals in allende type 1 chondrules have ferrous rims fa15 44 a few microns thick at grain surfaces and along crosscutting cracks this ferrous olivine contains as much as 2 atomic pet al and cr and 0 2 pct ti along cracks profiles of fe al cr and ti are consistent with difrusional emplacement these elements moved from an external source through the cracks as a vapor or by grain boundary diffusion then into the olivine by lattice diffusion the emplacement did not occur during an epoch of planetary metamorphism that partly equilibrated matrix and chondrule olivines because e g neither matrix nor primary magnesian chondrule olivine contains even 1 10 this much al cr and ti we argue that the source of these elements was the nebular gas and emplacement occurred prior to accretion the ferrous zones at olivine grain boundaries do not display simple diffusion profiles rather they appear to be a composite of two concentric rims the inner rims have compositions similar to those of the ferrous zones along cracks and contain the highest concentrations of al cr and ti the outer rims up to 20 m thick where grain boundaries are at the surfaces of chondrules are of uniformly high fa content and relatively low al cr and ti concentration these outer rims appear to be additional material that condensed onto the chondrules after the diffusional emplacement event discussed earlier matrix olivine grains which are identical to these rims in composition condensed simultaneously

observations of the internal tide in monterey canyon abstract data from two shipboard experiments in 1994 designed to observe the semidiurnal internal tide in monterey canyon reveal semidiurnal currents of about 20 cm s 1 which is an order of magnitude larger than the estimated barotropic tidal currents the kinetic and potential energy evidenced by isopycnal displacements of about 50 m was greatest along paths following the characteristics calculated from linear theory these energy ray paths are oriented nearly parallel to the canyon floor and may originate from large bathymetric features beyond the mouth of monterey bay energy propagated shoreward during the april experiment itex1 whereas a standing wave that is an internal seiche was observed in october itex2 the difference is attributed to changes in stratification between the two experiments higher energy levels were present during itex1 which took place near the spring phase of the fortnightly 14 8 days cycle in sea level while itex2 occurred close to the neap phase further evide

the oxygen isotope record in murchison and other carbonaceous chondrites the ranges of 18o and 17o in components of the murchison c2 chondrite exceed those in all other meteorites analyzed previous authors have proposed that c2 chondrites are the products of aqueous alteration of anhydrous silicates a model is presented to determine whether the isotopic variations can be understood in terms of such alteration processes the minimum number two of initial isotopic reservoirs is assumed two major stages of reservoir interaction are required one at high temperature to produce the16o mixing line observed for the anhydrous minerals and another at low temperature to produce the matrix minerals the isotopic compositions severely constrain the conditions of the low temperature process requiring temperatures 44 extension of the model to the data on c1 chondrites requires aqueous alteration in a warmer wetter environment

fayalitic olivine in cv3 chondrite matrix and dark inclusions a nebular origin fayalitic olivine fa32 is the major component of the matrices and dark inclusions of cv3 and other unequilibrated chondrites it occurs most commonly as rims veins and halos in and around chondrule silicates in the allende type cv3oxa chondrites and to a much lesser extent in the reduced cv3r and bali type cv3oxb chondrites the olivines have distinctive platy tabular and lath or irregular shaped crystals with the ratio of the two types varying widely in cv3oxb chondrites matrix fayalitic olivines range up to fag99 9 whereas in the other cv3 chondrites the range is much smaller the platy and tabular anisotropic forms of the fayalitic olivines strongly suggest growth from a vapor and the nature of the occurrences suggests that cv3 matrices are unequilibrated mixtures of nebular materials we argue that the parent body hydration dehydration model has numerous inconsistencies that make this hypothesis highly unlikely these include 1 there is no direct evidence linking fayalitic olivine to precursor phyllosilicates 2 dehydration of phyllosilicates cannot explain the wide range of morphologies of the fayalitic olivines 3 fayalitic olivine clearly predates the formation of the hydrous phases in cv3 chondrites and is one of the phases that breaks down to form phyllosilicates keller et al 1994 4 the unequilibrated nature of the matrix including fine scale zoning in 10 m sized fayalitic olivine crystals would not survive the parent body metamorphism required in the dehydration model 5 a dark inclusion in the ningqiang chondrite contains fayalitic olivine rimmed by glassy and microcrystalline material zolensky et al 1997 which probably formed by radiation damage this indicates that the fayalitic olivine was exposed to solar radiation in a nebular setting 6 some allende chondrules contain unaltered primary anhydrous glassy mesostasis in contact with the host matrix e g ikeda and kimura 1995 chondrule mesostases would not have survived parent body hydration without becoming hydrated and would probably not survive the metamorphic heating required in the dehydration scenario 7 single platy and barrel shaped crystals of fayalitic olivine are present in accretionary rims in calcium aluminum rich inclusions cais macpherson and davis 1997 which developed in the nebula 8 matrix lumps completely encased in chondrules in ordinary chondrites contain mainly fayalitic olivine scott et al 1984 which indicates a nebular origin 9 oxygen isotopic compositions of allende matrix and dark inclusions strongly indicate little or no hydration for allende and its components clayton 1997 we favor a nebular vaporization recondensation model in which vaporization of chondritic dust produced a fayalite rich vapor followed by formation of the fayalitic olivine by direct recondensation from the vapor epitactic growth on surfaces of existing forsterite and enstatite in chondrules and replacement of existing forsterite and enstatite by gas solid exchange

plagioclase rich chondrules in the reduced cv chondrites evidence for complex formation history and genetic links between calcium aluminum rich inclusions and ferromagnesian chondrules plagioclase rich chondrules prcs in the reduced cv chondrites efremovka leoville vigarano and grosvenor mountains gro 94329 consist of magnesian low ca pyroxene al ti cr rich pigeonite and augite forsterite anorthitic plagioclase feni metal sulfide nodules and crystalline mesostasis composed of silica anorthitic plagioclase and al ti cr rich augite the silica grains in the mesostases of the cv prcs are typically replaced by hedenbergitic pyroxenes whereas anorthitic plagioclase is replaced by feldspathoids nepheline and minor sodalite some of the prcs contain regions that are texturally and mineralogically similar to type i chondrules and consist of forsterite low ca pyroxene and abundant feni metal nodules several prcs are surrounded by igneous rims or form independent compound objects twelve prcs contain relic calcium aluminum rich inclusions cais composed of anorthite spinel high ca pyroxene forsterite and al rich low ca pyroxene anorthite of these cais is generally more heavily replaced by feldspathoids than anorthitic plagioclase of the host chondrules this suggests that either the alteration predated formation of the prcs or that anorthite of the relic cais was more susceptible to the alteration than anorthitic plagioclase of the host chondrules these observations and the presence of igneous rims around prcs and independent compound prcs suggest that the cv prcs may have had a complex multistage formation history compared to a more simple formation history of the cr prcs relatively high abundances of moderately volatile elements such as cr mn and si in the prcs suggests that these chondrules could not have been produced by volatilization of ferromagnesian chondrule precursors or by melting of refractory materials only we infer instead that prcs in carbonaceous chondrites formed by melting of the reduced chondrule precursors magnesian olivine and pyroxene feni metal mixed with refractory materials relic cais composed of anorthite spinel high ca pyroxene and forsterite the mineralogical chemical and textural similarities of the prcs in several carbonaceous chondrite groups cv co ch cr and common presence of relic cais in these chondrules suggest that prcs may have formed in the region s intermediate between the regions where cais and ferromagnesian chondrules originated

kinetics of diffusion controlled evaporation of fe mg olivine experimental study and implication for stability of fe rich olivine in the solar nebula abstract evaporation is a process that caused chemical fractionation in the solar nebula the evaporation rates of meteorite forming minerals and silicate melts are key parameters for constraining the timescale of high temperature processes in the early solar nebula and for understanding the mechanisms of cosmochemical fractionation the kinetics of evaporation of olivine initial fo 92 the most common silicate in meteorites was experimentally investigated at 1414 c for various duration under continuous evacuation the surface of olivine becomes more magnesian and the interior becomes zoned as evaporation proceeds indicating preferential evaporation of the fayalite fa component the weight loss surface composition and interior zoning profile were analyzed using a semi infinite one dimensional diffusion model with boundary migration and the controlling model parameters were optimized by fitting the experimental results the evaporation rate of olivine shows notable composition and orientation dependence as olivine becomes more magnesian the evaporation rates of the 100 010 and 001 surfaces decrease among which the rate at the 001 surface is greatest 1 0 m h at fo 91 8 which is about 2 orders of magnitude faster than that of pure synthetic forsterite the estimated fe mg fractionation factor shows anisotropy ranging from 0 017 to 0 035 which is significantly greater than the equilibrium value of the fe mg distribution coefficient between olivine and gas suggesting kinetic suppression of evaporation of the fa component the fe mg interdiffusion coefficient at 1414 c which also shows notable composition and orientation dependence is estimated to be 8 7 10 15 m2 sec along the c axis the results were applied to constrain the timescale of heating for a spherical fo50 olivine grain to retain the fa component olivine dust 1 m in diameter can retain 80 of the initial fa component for one minute in vacuum and for 30 min at 10 pa ph2 when heated at 1414 c therefore fo50 olivine in chondrite matrices could have survived an incipient heating event depending on the ambient hydrogen pressure if they were originally present in the solar nebula

phyllosilicates in the mokoia cv carbonaceous chondrite evidence for aqueous alteration in an oxidizing environment abstract most cv chondrites contain little if any phyllosilicate mineralization a petrographic and transmission electron microscopy study of the mokoia cv carbonaceous chondrite shows that the matrix chondrules aggregates and inclusions all contain considerable amounts of phyllosilicates those in the matrix are mostly fe bearing saponite while those in chondrules aggregates and inclusions are both febearing saponite and na rich phlogopite serpentine occurs as minor coherent intergrowths within the phlogopite the saponite resulted from aqueous alteration of fe rich olivine and the phlogopite resulted from alteration of ca rich clinopyroxene anorthite spinel and ca al si rich glass iron rich olivines in the mokoia matrix contain extremely thin planar zones parallel to 100 with diffuse streaks along a in their diffraction patterns such planar zones are not known from terrestrial olivines saponite forms preferentially along these zones with its 001 planes roughly parallel to olivine 100 the planar zones probably consist of precipitates of fe oxide or fe hydroxide that were produced during oxidation of olivine while it cooled from a high temperature by formation of the fe rich precipitates olivine became fe deficient and thus was structurally disturbed during subsequent hydration saponite formed by preferentially replacing these regions in olivine simultaneously part of the fe was mobilized and precipitated as magnetite along the olivine peripheries the mineralogy and occurrence of phyllosilicates in mokoia differ from those in the ci and cm chondrites the differences suggest that aqueous alteration of the three meteorite groups probably occurred under a variety of conditions

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

phosphate minerals in ll chondrites a record of the action of fluids during metamorphism on ordinary chondrite parent bodies ordinary chondrites contain two phosphate minerals merrillite and chlorapatite both of which are secondary minerals that developed in response to metamorphism on the chondrite parent bodies we have studied the phosphate mineralogy of four ll chondrites of petrologic types 3 9 6 in order to determine the petrogenesis of the two minerals and interpret the conditions under which they formed characterization of merrillite and apatite includes textural observations mineral compositions determined by electron probe microanalysis and ion microprobe analyses of trace element and volatile anion elemental abundances initial formation of phosphate minerals during mild metamorphism to petrologic type 4 conditions resulted in oxidation of p that was originally incorporated in metal and growth of merrillite as inclusions within metal grains subsequent development of both phosphate minerals occurred in response to diffusional equilibration possible precipitation from fluids as well as replacement reactions resulting from interactions with fluids porosity and vein filling textures in both merrillite and chlorapatite as well as textures indicating replacement of merrillite by chlorapatite support a model in which fluid played a significant role and suggest an interface coupled dissolution reprecipitation mechanism during metasomatism some associations of phosphate minerals with chromite plagioclase assemblages suggest that phosphate minerals could also be related to impact processes either as precipitation from an impact melt or as a result of interactions with a fluid or vapor derived from an impact melt fluid compositions may have been water bearing initially at low temperatures of metamorphism but later evolved to become halogen rich and very dry late stage halogen rich fluids that dominated during cooling of ll chondrite material may have been derived from vaporization of partial melts in the interior of the parent body overall the ll chondrite parent body underwent a complex chemical evolution in which metasomatism played a significant role

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

relationship among o mg isotopes and the petrography of two spinel bearing compound chondrules the petrological properties and o and al mg isotopic compositions of two spinel bearing chondrules from the allende cv chondrite were investigated using scanning electron microscopy and secondary ion mass spectrometry a coarse spinel grain in a barred olivine bo chondrule is less enriched in 16o 17o 5 17o 17o 0 52 18o whereas smaller spinel grains in a plagioclase rich chondrule member of a compound chondrule are extremely 16o rich 17o 17 and the spinels have a strongly serrated character the petrological features and 16o enrichments of the spinels in the plagioclase rich chondrule indicate that spinels originating in coarse grained ca al rich inclusions cais were incorporated into chondrule precursors and survived the chondrule forming event the degree of 16o excesses among minerals within each chondrule is correlated to the crystallization sequences this evidence suggests that the o isotopic variation among minerals may have resulted from incomplete exchange of o isotopes between 16o rich chondrule melt and 16o poor nebular gas aqueous alteration also has changed the o isotope compositions in the mesostasis the feldspathic mesostasis in the bo chondrule shows a disturbed mg al isochron indicating that the bo chondrule experienced secondary alteration while plagioclase in the plagioclase rich chondrule member of the compound chondrule shows slight 26mg excesses corresponding to 26al 27al 0 4 6 4 0 2 10 6 nepheline formed by secondary alteration shows no detectable excess the al mg isotopic system of these chondrules was disturbed by aqueous alteration and thermal metamorphism on the allende parent body

organic matter and metamorphic history of co chondrites abstract the metamorphic grades of a series of eight co3 chondrites alha77307 colony kainsaz felix lance ornans warrenton and isna have been quantified the method used was based on the structural grade of the organic matter trapped in the matrix which is irreversibly transformed by thermal metamorphism the maturation of the organic matter is independent with respect to the mineralogical context and aqueous alteration this metamorphic tracer is thus valid whatever the chemical class of chondrites moreover it is sensitive to the peak metamorphic temperature the structural grade of the organic matter was used along with other metamorphic tracers such as petrography of opaque minerals fa and fs silicate composition in type i chondrules presolar grains and noble gas p3 component abundance the deduced metamorphic hierarchy and the attributed petrographic types are the following alha77307 3 03 for most metamorphosed objects the peak metamorphic temperature can be estimated using a geothermometer calibrated with terrestrial metasediments beyssac o goffe b chopin c and rouzaud j n 2002 raman spectrum of carbonaceous material in metasediments a new geothermometer j metamorph geol 20 859 871 a value of 330 c was obtained for allende cv chondrite warrenton and isna consistent with temperatures estimated from fe diffusion weinbruch s armstrong j and palme h 1994 constraints on the thermal history of the allende parent body as derive from olivine spinel thermometry and fe mg interdiffusion in olivine geochim cosmochim acta 58 2 1019 1030 from the ni content in sulfide metal assemblages zanda b bourot denise m and hewins r 1995 condensate sulfide and its metamorphic transformations in primitive chondrites meteorit planet sci 30 a605 and from the d002 interlayer spacing in poorly graphitized carbon rietmeijer f and mackinnon i 1985 poorly graphitized carbon as a new cosmothermometer for primitive extraterrestrial materials nature 315 733 736 the trapped noble gas and c content appear to be sensitive but not precise metamorphic tracers indicating that the ornans paradox does not exist major problems with the current petrologic types derived from induced thermoluminescence are pointed out

are c1 chondrites chemically fractionated a trace element study abstract six c1 chondrite samples and a c2 xenolith from the plainview h5 chondrite were analyzed by radiochemical neutron activation for the elements ag au bi br cd ce cs eu ge in ir lu nd ni os pd pt rb re sb se sn tb te tl yb and zn the data were combined with 9 earlier analyses from this laboratory and examined for evidence of chemical fractionation in c1 chondrites a number of elements br rb cs au re os ni pd sb bi in te show small but correlated variations those of the first 8 probably reflect hydrothermal alteration in the meteorite parent body whereas those of sb bi in and te may at least in part involve nebular processes br and au show systematic abundance differences from meteorite to meteorite which suggests hydrothermal transport on a kilometer scale the remaining elements vary from sample to sample suggesting transport on a centimeter scale there is no conclusive evidence for nebular fractionation affecting c1 s though c1 chondrites have lower zr hf and ir re ratios than do other chondrite classes these ratios vary in other classes suggesting that those classes rather than c1 s are fractionated three fractionation prone ree ce eu and yb have essentially the same relative abundances in c1 s and all other chondrite classes and hence apparently are not fractionated in c1 s we did not confirm the large tb and yb variations in c1 s reported by other workers we present revised mean c1 abundances for 35 elements based on the new data and a critical selection of literature data changes are generally less than 10 except for br rb ag sb te au and the ree the plainview c2 xenolith has normal trace element abundances except for 3 elements falling appreciably above the c2 range rb cs and bi hydrothermal alteration may be the reason for all 3 though nebular fractionation remains a possibility for bi

hydrologic cycling over antarctica during the middle miocene warming global warmth 20 15 million years ago allowed vegetation to grow on formerly ice covered areas of antarctica leaf wax and pollen data show that this growth was supported by increased hydrologic activity over the antarctic coast derived from a local moisture source

sulfur release from the columbia river basalts and other flood lava eruptions constrained by a model of sulfide saturation abstract a very likely cause of widespread environmental impacts of flood basalt eruptions is the emission of sulfur chlorine and possibly fluorine from the erupting magma we present new data on the s contents of rare glass inclusions and matrix glasses preserved in quenched lava selvages from lava fields of the columbia river basalt group crbg ginkgo sand hollow and sentinel gap flows wanapum basalt formation we compare these results with published data from neral and jawar formation lavas deccan traps india and the roza flow crbg crbg glass inclusions have up to 2000 ppm s and 15 16 wt feototal by contrast the deccan examples have about 1400 ppm s and 10 wt feototal several of the glass inclusions are partly degassed indicating entrapment during magma rise and matrix glasses are typically more evolved than glass inclusions due to small amounts of in situ crystallization using only the highest s inclusions and taking account of the effect of in situ crystallization and degassing on the s content of the residual matrix glasses indicates s yields of about 0 07 to 0 1 wt from deccan eruptions and about 0 15 wt from wanapum crbg eruptions the pre eruptive s contents of these magmas correlate with weight feototal in the same way as undegassed sulfide saturated mid ocean ridge basalts using oceanic basalts to define a sulfide saturation line and data on s contents of degassed basalts we propose an equation to estimate the weight s yield s from initially sulfide saturated basalt liquid without the need to find well preserved rare undegassed glass inclusions and matrix glasses s 0 0 1418 feo total 0 0 6381 0 0 2635 this compares well with independent estimates derived from the petrologic method by taking the difference in s concentration of glass inclusions and matrix glass applying our method to the aphyric grande ronde basalts of the crbg implies a total yield of about 1000 gt so2 delivered into the miocene atmosphere in intermittent bursts of

nepheline and sodalite in the matrix of the ningqiang carbonaceous chondrite implications for formation through parent body processes abstract ningqiang is an ungrouped carbonaceous chondrite that chemically and petrologically resembles cv3 chondrites the matrix of ningqiang shows much higher abundances of na k and al by factors of 4 4 2 7 and 1 6 respectively than in cv3 chondrites our scanning and transmission electron microscope observations and synchrotron radiation x ray diffraction measurements reveal that the major proportions of these elements can be attributed to the presence of nepheline and sodalite rietveld refinement of x ray diffraction data shows that the feldspathoids constitute 7 7 vol of all crystalline phases in the matrix nepheline and sodalite occur mostly as discrete equidimensional grains 2 5 m in diameter that are dispersed homogeneously in the matrix most of the grains contain inclusions of fe rich olivine and minor ca pyroxene magnetite troilite and pentlandite despite the high abundances of na k and al in the matrix of ningqiang the bulk meteorite abundances of these elements are comparable to those of the cv group e g rubin et al 1988 this means that the chondrules which constitute a major proportion of the volume other than the matrix in ningqiang are depleted in na k and al in fact our analyses and observations show that the chondrules in ningqiang overall contain very small amounts of these elements our interpretation of these findings suggests that nepheline and sodalite in the ningqiang matrix were originally formed by na metasomatism of the chondrules and ca al rich inclusions in the meteorite parent body afterward they were likely disaggregated and scattered into the matrix however it is difficult to envisage that the disaggregation and scattering occurred in situ in the present setting of the meteorite hence we suggest that the ningqiang meteorite underwent these processes before final lithification

revised conceptual model for maar diatremes subsurface processes energetics and eruptive products diatremes are debris filled structures beneath maars that result from many magma water phreatomagmatic explosions during a monogenetic volcano s lifetime a long standing model requires deepening explosions due to water table drawdown that eject progressively deeper seated country rock from the explosion sites while the overlying diatreme and its surface crater widen due to subsidence a revised model is proposed wherein explosions can take place at any level within a diatreme at a given time most effectively venting material from near surface explosions deep seated country rock lithics in tephra deposits record stepwise vertical mixing of material by upward directed debris jets and downward subsidence rather than direct ejection from deep explosions juvenile and lithic clasts erupted during a given explosion may have had a complex history within the diatreme and need not directly reflect fragmentation or brecciation during the explosion that ejects them

barotropic semidiurnal tidal currents off northern california during the coastal ocean dynamics experiment code barotropic semidiurnal tidal currents measured off the coast of northern california during the coastal ocean dynamics experiment code are examined while the pressure field is consistent with the idea that the semidiurnal surface tide is dominated by a kelvin wave a high degree of variability over alongshore distances of the order of 25 km is observed in the velocity field comparison with existing models used to predict tidal velocities from sea level measurements cannot account for this spatial structure perturbation analysis of a kelvin wave propagating along a coastal boundary with bumps characterized by an alongshore length scale much less than the rossby radius of deformation shows effects on the velocity and pressure field which decay offshore with the alongshore scale of the bumps the effect on the velocity field exceeds that on the pressure field by a factor equal to the ratio of the rossby radius to the alongshore scale of the bumps we conclude that the alongshore structure observed in the measured barotropic semidiurnal tidal currents may be due in part to the local variations in the coastline geometry in the code region

selective environmental stress from sulphur emitted by continental flood basalt eruptions several biotic crises during the past 300 million years have been linked to episodes of continental flood basalt volcanism and in particular to the release of massive quantities of magmatic sulphur gas species flood basalt provinces were typically formed by numerous individual eruptions each lasting years to decades however the environmental impact of these eruptions may have been limited by the occurrence of quiescent periods that lasted hundreds to thousands of years here we use a global aerosol model to quantify the sulphur induced environmental effects of individual decade long flood basalt eruptions representative of the columbia river basalt group 16 5 14 5 million years ago and the deccan traps 65 million years ago for a decade long eruption of deccan scale we calculate a decadal mean reduction in global surface temperature of 4 5 k which would recover within 50 years after an eruption ceased unless climate feedbacks were very different in deep time climates acid mists and fogs could have caused immediate damage to vegetation in some regions but acid sensitive land and marine ecosystems were well buffered against volcanic sulphur deposition effects even during century long eruptions we conclude that magmatic sulphur from flood basalt eruptions would have caused a biotic crisis only if eruption frequencies and lava discharge rates had been high and sustained for several centuries at a time

fayalite rich rims veins and halos around and in forsteritic olivines in cais and chondrules in carbonaceous chondrites types compositional profiles and constraints of their formation abstract fayalite rich rims veins and halos around and in forsteritic olivines are a wide spread phenomenon in chondrules ca al rich inclusions cais and single grains in carbonaceous chondrites the presence of fayalite rod like crystals and laths in rims veins in wall of pores and as fluffy network bridging neighbouring olivines pyroxenes feldspars etc is strongly suggestive that the fayalitic olivine was formed by condensation presumably from the solar nebula gas the formation of the fayalitic olivine was probably caused by an increase in the h 2 o h 2 ratio to a ratio between 0 1 1 subsequent to condensation of forsterite at that stage feni inclusions in olivine were also oxidized and fayalitic halos around the metal were then formed by fe diffusion along with addition of sio 2 from the solar gas or loss of mgo to the solar gas the fa rich olivine rims and veins display a narrow compositional variation between fa 34 and fa 46 subsequent to condensation of fa rich olivine and oxidation of feni metal fe diffused in forsterite this diffusion was probably enhanced due to the presence of point defects in olivine or the formation of a nonstoichiometric phase analogous to laihunite enriched in al 2 o 3 and cr 2 o 3 however the presence of al 2 o 3 and cr 2 o 3 rich discrete domains cannot be excluded cooling rates calculated by modelling of the diffusion profiles are indicative of rapid cooling subsequent to the condensation of fayalitic olivines we obtain cooling rates ranging from 2000 c day and 10 c day at an initial temperature of 1200 c and 900 c respectively

chemical and physical studies of type 3 chondrites v the enstatite chondrites abstract we report instrumental neutron activation analysis determinations of 19 major minor and trace elements in three enstatite chondrites based on these and literature data on the bulk and mineral composition of enstatite chondrites we discuss the history of the type 3 or unequilibrated enstatite chondrites and their relationship with the other enstatite chondrites the type 3 enstatite chondrites have e chondrite lithophile element abundances and their siderophile element abundances place them with the eh chondrites well resolved from the el chondrites moderately volatile chalcophile elements are at the low end of the eh range and cr appears to be intermediate between eh and el we suggest that the type 3 enstatite chondrites are eh chondrites which have suffered small depletions of certain chalcophile elements through the loss of shock produced sulfurous liquids the oxygen isotope differences between type 3 and other enstatite chondrites is consistent with equilibration with the nebula gas 30 higher than the others or with the loss of a plagioclase rich liquid the mineral chemistry of the type 3 chondrites is consistent with either low temperature equilibration or in some instances with shock effects

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

olivine rich rims surrounding chondrules in the mokoia cv3 carbonaceous chondrite further evidence for parent body processes abstract fine grained rims surrounding chondrules and inclusions in the mokoia cv3 carbonaceous chondrite can be divided into phyllosilicate rich and olivine rich types we present a petrographic and electron microscopic study of the olivine rich rims and their host objects referred to as chondrules olivine rich rims the olivine rich rims consist mainly of fe rich olivine and very minor phyllosilicate saponite their host chondrules contain minor saponite and phlogopite which resulted from aqueous alteration of anhydrous silicates mineralogical and compositional characteristics of the chondrules olivine rich rims suggest that they experienced mild thermal metamorphic effects the rims commonly contain veins of coarse grained fe rich olivine magnetite and fe ni sulfides the chondrules show abundant evidence of alteration along their peripheries and the alteration textures suggest a mechanism for rim formation by replacement of the chondrules initially enstatite and opaque nodules preferentially reacted to form coarse platy fe rich olivine crystals which were subsequently divided into finer grains forsterite was also replaced by fe rich olivine as the alteration advanced these fe rich olivines were disaggregated mixed with simultaneously produced saponite and formed rims in contrast the surrounding matrix shows no evidence of such alteration and metamorphism these observations indicate that the chondrules olivine rich rims did not experience these secondary processes in their present setting the results suggest that the chondrules olivine rich rims experienced extensive replacement reactions in an environment in which aqueous fluids existed but only in minor amounts they have probably also undergone simultaneous and or subsequent mild thermal metamorphism we suggest that the chondrules olivine rich rims are actually clasts transported from a relatively dry region in the parent body that was different from the region where mokoia was finally lithified

tidal and buoyancy driven currents in chignecto bay bay of fundy circulations in the chignecto bay system upper part of the bay of fundy were studied using current meter moorings tidal and diagnostic models and salinity and suspended sediment concentration measurements the current meter observations revealed that 1 the tides behaved basically as standing waves tidal current leads tidal elevation by about 90 2 tidal currents were typically of the order of 1 m s 1 and were almost rectilinear 3 residual currents were up to 0 17 m s 1 and the circulation pattern was quite complex and 4 a two layer residual circulation with inflow in the upper layer and outflow in the lower layer existed at the entrance to the bay most of the residual currents in the upper part of the bay were driven by tidal rectification the two layer residual circulation at the bay entrance was examined using a diagnostic model it was found that the circulation was probably induced by horizontal density variations near the entrance to cumberland basin shepody bay and chignecto bay the cross channel variation of surface suspended sediment concentration was consistent with the observed residual currents from current meter moorings and the estimated currents from the diagnostic model the cross channel variation of salinity near the entrance to chignecto bay was also consistent with the observed and computed residual currents

the structure of three dimensional tide generating currents experimental verification of a theoretical model in an earlier paper tee 1979 a simple model for computing the three dimensional structure of the tidal current in a well mixed water column was presented to examine the validity of the theoretical model 12 current meters were moored at three locations at the head of the bay of fundy four meters were moored in each location at different depths in order to investigate the significance of the small semi minor axis and the small vertical variation of phase and inclination of the semi major axis the error of the analysed harmonic constants has been examined in detail new formulas for estimating the error for non separated constituents and for the semi major axis semi minor axis and the phase and inclination of the semi major axis have been derived a discussion of when the simple formulas for limiting cases can be applied has also been included by comparing the analysed coefficients with tee s 1979 simple model it was found that by using realistic forms of the vertical eddy viscosity the simple theoretical model reproduced the observed vertical variation of the tidal currents in the well mixed estuary reasonably well

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

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

aqueous alteration of the bali cv3 chondrite evidence from mineralogy mineral chemistry and oxygen isotopic compositions abstract a petrographic geochemical and oxygen isotopic study of the bali cv3 carbonaceous chondrite revealed that the meteorite has undergone extensive deformation and aqueous alteration on its parent body deformation textures are common and include flattened chondrules a well developed foliation and the presence of distinctive 100 planar defects in olivine the occurrence of alteration products associated with the planar defects indicates that the deformation features formed prior to the episode of aqueous alteration the secondary minerals produced during the alteration event include well crystallized mg rich saponite framboidal magnetite and ca phosphates the alteration products are not homogeneously distributed throughout the meteorite but occur in regions adjacent to relatively unaltered material such as veins of altered material following the foliation the alteration assemblage formed under oxidizing conditions at relatively low temperatures oxygen isotopic compositions for unaltered regions in bali fall within the field for other cv3 wholerocks however the oxygen isotopic compositions of the heavily altered material lie in the region for the cm and cr chondrites the heavy isotope enrichment of the altered regions in bali suggest alteration conditions similar to those for the petrographie type 2 carbonaceous chondrites

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

record of low temperature alteration in asteroids most chondritic materials experienced diverse styles of secondary alteration resulting in formation of hydrous and anhydrous oxygen bearing minerals silicates oxides and carbonates phyllosilicates magnetite calcite dolomite breunnerite ferrous olivine hedenbergite wollastonite grossular monticellite forsterite andradite nepheline sodalite brearley 2003 2005 and references therein petrographic mineralogic oxygen and short lived isotope systematics 26al 26mg 53mn 53cr 129i 129xe suggest that alteration occurred in the presence of aqueous solutions under variable physico chemical conditions temperature water rock ratio ph f o2 and fluid compositions in an asteroidal setting it started within 1 2 m y after formation of the cv cais was multistage and lasted up to 15 m y krot et al 2006 and references therein here we review bulk o isotopic compositions of chondritic materials o isotopic compositions of secondary minerals produced during asteroidal alteration and possible effects of fluid assisted thermal metamorphism on o isotopic exchange in primary high temperature minerals melilite and anorthite in the cv and co cais the implications of these data for understanding temperatures of alteration water rock ratios and oxygen isotopic composition of water that probably accreted into chondrite parent bodies in the form of ice are discussed the inferred or measured o isotopic composition of the meteoritic water is close to the terrestrial fractionation line 17o 2 it is very different from the inferred o isotopic compositions of the sun 17o 25 clayton 2002 yurimoto and kuramoto 2004 hashizume and chaussidon 2005 lyons and young 2005 suggesting significant evolution of o isotopic composition of the gaseous reservoir in the inner protoplanetary disk over its short 3 5 m y life time

astronomic calibration of the late oligocene through early miocene geomagnetic polarity time scale at ocean drilling program odp site 1090 subantarctic south atlantic benthic foraminiferal stable isotope data from cibicidoides and oridorsalis span the late oligocene through early miocene f24 16 ma at a temporal resolution of f5 ky over the same interval a magnetic polarity stratigraphy can be unequivocally correlated to the geomagnetic polarity time scale gpts thereby providing direct correlation of the isotope record to the gpts in an initial age model we use the newly derived age of the oligocene miocene o m boundary of 23 0 ma of shackleton et al geology 28 2000 447 revised to the new astronomical calculation la2003 of laskar et al icarus in press to recalculate the spline ages of cande and kent j geophys res 100 1995 6093 we then tune the site 1090 y 18 o record to obliquity using la2003 in this manner we are able to refine the ages of polarity chrons c7n through c5cn 1n the new age model is consistent within one obliquity cycle with previously tuned ages for polarity chrons c7n through c6bn from shackleton et al geology 28 447 450 2000 when rescaled to la2003 the results from site 1090 provide independent evidence for the revised age of the oligocene miocene boundary of 23 0 ma for early miocene polarity chrons c6aar through c5cn our obliquity scale age model is the first to allow a direct calibration to the gpts the new ages are generally within one obliquity cycle of those obtained by rescaling the cande and kent j geophys res 100 1995 6093 interpolation using the new age of the o m boundary 23 0 ma and the

the age of the steens reversal and the columbia river basalt group abstract the columbia river basalt group crbg eruptions have a well defined relative magnetostratigraphy but have not been definitively correlated to the geomagnetic polarity time scale 40 ar 39 ar ages are presented from lavas erupted in the r 0 through n 1 magnetozones of the crbg and in the transition between r 0 and n 0 four ages from transitionally magnetized lava flows at steens mountain catlow peak and poker jim ridge with a weighted mean age 16 58 0 10 ma 1 and the more precise age 16 654 0 025 ma of the normally magnetized oregon canyon tuff at the top of the catlow peak section show that the oldest crbg magnetozone r 0 correlates with the c5cr chron bayesian statistical analysis applied to data from four flows at catlow peak using the mean age of the steens reversal gives a best and preferred age of the steens reversal of 16 73 0 13 0 08 ma 95 confidence depending on the geomagnetic polarity time scale model the eruption rate from n 0 through r 2 0 34 0 45 ma in the middle and the bulk of the crbg emplacement averaged 0 30 0 41 km 3 a and peaked at a rate 1 1 2 to 4 1 2 times higher during r 2

fabric analysis of allende matrix using ebsd fabric analysis of the interstitial matrix material in primitive meteorites offers a novel window on asteroid formation and evolution electron backscatter diffraction ebsd has allowed fabrics in these fine grained materials to be visualized in detail for the first time our data reveal that allende a cv3 chondrite possesses a uniform planar short axis alignment fabric that is pervasive on a broad scale and is probably the result of deformational shortening related to impact or gravitational compaction interference between this matrix fabric and the larger more rigid components such as dark inclusions dis and calcium aluminium rich inclusions cais has lead to the development of locally oriented and intensified matrix fabrics in addition dis possess fabrics that are conformable with the broader matrix fabric these results suggest that dis were in situ prior to the deformational shortening event responsible for these fabrics thus providing an argument against dark inclusions being fragments from another lithified part of the asteroid kojima and tomeoka 1996 fruland et al 1978 moreover both dis and allende matrix are highly porous 25 corrigan et al 1997 mobilizing a highly porous di during impact induced brecciation without imposing a fabric and incorporating it into a highly porous matrix without significantly compacting these materials is improbable we favor a model that involves allende dis cais and matrix accreting together and experiencing the same deformation events

new insights into the formation of fayalitic olivine from allende dark inclusions abstract although considerable progress has been made in unraveling the origin s of fayalitic olivines in dark inclusions dis many questions remain still unresolved and or controversial we combine a chemical and petrographic study of the allende dark inclusion 4884 2b amnh new york and atem studies of a fragment of the dark inclusion allende af nhm vienna and discuss an alternative way in which fayalitic olivines could have formed allende dark inclusion 4884 2b contains a few aggregates with variable proportions of transparent and feathery olivine two such objects aggregates a and b are the focus of this study as they preserve glasses that can help in deciphering the nature of the processes involved during olivine growth and subsequent olivine transformation the petrographic and chemical characteristics of aggregates a and b indicate that the forsteritic stack olivines may be pseudomorphs of clear olivine crystals the atem studies in all af suggest that fayalitic olivines may be the result of secondary processes e g metasomatic exchange reactions operating in the solar nebula transformation may have occurred through the mediation of a dry gas phase involving nonvolatile major elements such as mg and fe e g dohmen et al 1998 this mechanism could reveal olivine growth patterns e g stacked platelets due to a rapid growth regime and may have contributed to the development of their fibrous aspect while preserving the shape i e volume of the crystals this highly selective process did completely or partially transform ferromagnesian minerals but affected the fine grained mesostasis only slightly

oxygen isotopic distribution in an amoeboid olivine aggregate from the allende cv chondrite primary and secondary processes the oxygen isotopic distribution in an amoeboid olivine aggregate aoa tta1 02 from the allende cv3 chondrite has been determined by secondary ion mass spectrometry the irregular shaped tta1 02 5 3mm consists mostly of olivine grains of ca 5 m in diameter olivine grains of mg rich fo95 and fe rich fo60 composition are in direct contact with each other with a sharp compositional boundary oxygen isotopic compositions of fe rich olivine grains are 16o poor 17o 5 whereas mg rich olivine is 16o rich 17o 25 several al rich inclusions ca 500 m in diameter are enclosed by olivine grains in the aoa oxygen isotopic compositions of spinel and fassaite in al rich inclusions are 16o rich 17o 20 whereas those of anorthite nepheline and phyllosilicate are 16o poor 17o 5 we propose the following sequence of events during the formation of aoas in the allende meteorite 1 formation of al rich inclusions with 16o rich oxygen isotopic composition 2 accretion of mg rich olivine grains with 16o rich oxygen isotopic composition around al rich inclusions 3 accretion into parent body and 4 aqueous alteration in the parent body which led to crystallization of 16o poor minerals fe rich olivine anorthite nepheline and phyllosilicate this is reflecting reactions among primary 16o rich aoa minerals and aqueous fluid having 16o poor oxygen isotopic composition fe rich olivine grains precipitated from aqueous fluids which partially dissolved pre existing mg rich olivine grains sintering and mg fe diffusion occurred during thermal metamorphism anorthite nepheline and phyllosilicate in al rich inclusions replaced primary anorthite or melilite during the aqueous alteration stage

volatile fluxes during flood basalt eruptions and potential effects on the global environment a deccan perspective abstract we examine the role that flood basalt eruptions may have played during times of mass extinction through the release of volcanic gases continental flood basalt provinces have formed by numerous eruptions over a short period of geologic time characteristically a few million years within this period a short lived climactic phase that lasts about 1 ma typically emplaces a large proportion of the lava volume this phase consists of a series of huge eruptions each yielding 10 3 10 4 km 3 of magma each eruption lasted on the order of a decade or more and built an immense p hoehoe dominated lava flow field by eruptive activity along fissures tens to hundreds of km long high fire fountains emanating from vents along the fissures at times sustained eruption columns that lofted gas and ash into the upper troposphere and lower stratosphere while the lava flows covered huge areas the combination of large eruption magnitudes maintained high effusion rates during eruptions and the repeated nature of the characteristic large scale eruptive activity occurs in earth history only during periods of flood basalt volcanism based on recent analogs and determination of volatile contents of ancient flood basalt lavas we estimate that individual eruptions were capable of releasing 10 000 tg of so 2 resulting in atmospheric loadings of 1000 tg a 1 during a sustained decade long eruptive event we apply this model of flood basalt volcanism to estimate the potential mass of co 2 and so 2 released during formation of the 65 ma deccan province the deccan lava pile contains the record of hundreds of enormous p hoehoe flow fields erupted within a period of about 1 ma consequently atmospheric perturbations associated with so 2 emissions from just one of these long lasting eruptions were likely to have been severe and constantly augmented over a decade or longer by contrast the amounts of co 2 released would have been small compared with the mass already present in the atmosphere and thus much more limited in effect individual eruptions were followed by hiatuses of hundreds to thousands of years during which the gas contributions to the atmosphere would be recycled it is clear that the nature and potential atmospheric impact of a series of huge volume repeated long term degassing events requires further investigation in conjunction with appropriate climate models

late stage high temperature processesing in the allende meteorite record from ca fe rich silicate rims around dark inclusions secondary ca fe rich minerals cfm diopside hedenbergite andradite wollastonite kirschteinite are widespread in the allende carbonaceous chondrite about 90 vol of the total cao content of the allende matrix is concentrated in cfm the conditions and environment solar nebular or asteroidal of this alteration are still matters of controversial scientific discussion here we present evidence for late stage high temperature processes recorded in ca fe rich rims around allende dark inclusions 3529 and iv 1 studied using scanning sem and transmission electron microscopy tem and electron probe microanalysis the rims show a multilayered structure with the outermost layer intergrown with the matrix olivines and chondrule fragments of the allende host indicative of in situ formation the central portion of the rim around iv 1 contains several wollastonite polytypes a polysynthetically twinned polytype of pseudowollastonite wollastonite 2m and wollastonite 1t and an intergrowth of hedenbergite pm primitive monoclinic and augite hedenbergite ss these findings require temperatures above 1000 c and fast cooling rates after formation of the central part of the rim the close occurrences of three different polymorphs of wollastonite suggest that this process was highly localized and may have resulted from shock metamorphism

sulphur release from flood lava eruptions in the veidivotn grimsvotn and katla volcanic systems iceland book description humans have long marvelled at and feared the odorous and colourful manifestations of volcanic emissions and in some cases have harnessed them for their economic value the degassing process responsible for these phenomena is now understood to be one of the key factors influencing the timing and nature of volcanic eruptions moreover the surface emissions of these volatiles can have profound effects on the atmospheric and terrestrial environment and climate even more fundamental are the relationships between the history of planetary outgassing differentiation of the earth s interior chemistry of the atmosphere and hydrosphere and the origin and evolution of life this book provides a compilation of 23 papers that investigate the behaviour of volatiles in magma the feedbacks between degassing and magma dynamics and the composition flux and environmental atmospheric and climatic impacts of volcanic gas emissions

indicators of aqueous alteration and thermal metamorphism on the cv parent body microtextures of a dark inclusion from allende abstract an unusual dark clast in the allende cv3 chondrite termed allende af which was previously interpreted as a primary aggregate formed in the solar nebula kurat et al 1989 palme et al 1989 was re examined our study reveals abundant evidence suggesting that it probably experienced extensive aqueous alteration and subsequent thermal metamorphism on the meteorite parent body allende af contains numerous rounded to oval shaped inclusions embedded in a dark matrix the inclusions consisting predominantly of fine grains of fe rich olivine have internal textures suggesting that they are pseudomorphs after chondrules several inclusions appear to be replaced cais veins filled with fibrous olivine grains occur abundantly in both inclusions and matrix some veins up to 4 mm in length penetrate several inclusions providing strong evidence that aqueous alteration occurred after accretion the fibrous morphology of olivine in veins and inclusions suggests that the olivine was produced by dehydration and thermal transformation of phyllosilicate that had been formed by aqueous alteration olivine grains in the matrix contain numerous micro inclusions of fe ni sulfide which were probably incorporated during transformation from phyllosilicate allende af is probably related to the fine grained variety of dark inclusions reported from cv3 chondrites that has been described as the type containing abundant porous aggregates of fe rich olivine by johnson et al 1990 many dark inclusions previously described appear to be similar in texture and mineralogy to allende af and probably experienced similar secondary process on the meteorite parent body the wide variation in texture of dark inclusions can be explained by different degrees of aqueous alteration that preceded thermal metamorphism the size distribution of chondrule pseudomorphs and the abundance of cai pseudomorphs suggest that the precursor of allende af is a cv type chondrite probably allende itself oxygen isotopic and chemical compositions are consistent with this interpretation the cv parent body has been commonly thought to have escaped major secondary processing however allende af provides evidence that extensive aqueous alteration and thermal metamorphism have occurred locally on the cv parent body

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

quickly erupted volcanic sections of the steens basalt columbia river basalt group secular variation tectonic rotation and the steens mountain reversal 1 the steens basalt now considered part of the columbia river basalt group crbg contains the earliest eruptions of this magmatic episode lava flows of the steens basalt cover about 50 000 km2 of the oregon plateau in sections up to 1000 m thick the large number of continuously exposed quickly erupted lava flows some sections contain over 200 flows allows for small loops in the magnetic field direction paths to be detected for volcanic rocks this detail and fidelity are rarely found outside of the holocene and yield estimates of eruption durations at our four sections of 2 5 ka for 260 m at pueblo mountains 0 5 to 1 5 ka for 190 m at summit springs 1 3 ka for 170 m at north mickey and 3 ka for 160 m at guano rim that only one reversal of the geomagnetic field occurred during the eruption of the steens basalt the steens reversal at approximately 16 6 ma is supported by comparing 40ar 39ar ages and magnetic polarities to the geomagnetic polarity timescale at summit springs two 40ar 39ar ages from normal polarity flows 16 72 0 29 ma 16 61 and 16 92 0 52 ma 16 82 equals 2 error place their eruptions after the steens reversal while at pueblo mountains an 40ar 39ar age of 16 72 0 21 ma 16 61 from a reverse polarity flow places its eruption before the steens reversal paleomagnetic field directions yielded 50 nontransitional directional group poles which combined with 26 from steens mountain provide a paleomagnetic pole for the oregon plateau of 85 7 n 318 4 e k 15 1 a95 4 3 comparison of this new pole with a reference pole derived from crbg flows from eastern washington and a synthetic reference pole for north america derived from global data implies relative clockwise rotation of the oregon plateau of 7 4 5 0 or 14 5 5 4 respectively probably due to northward decreasing extension of the basin and range

chemical discrimination of columbia river basalt flows 1 the homogeneity and distinctive chemical composition of individual columbia river basalt flows are illustrated in a series of chemical plots and the procedure for flow identification is outlined the unique characterization of many individual eruptions permits units to be mapped from feeder dike to flow margins across the columbia plateau for hundreds of kilometers and so provides critical constraints on the physical and chemical evolution of this continental flood basalt province

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

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

sodium metasomatism in chondrules in co3 chondrites relationship to parent body thermal metamorphism we have studied the mineralogy and petrology of mesostases of 783 type i chondrules in seven co3 chondrites that range in petrologic subtype from 3 0 to 3 7 chondrule mesostases in the co chondrite of subtype 3 0 consist mainly of primary glass and plagioclase while chondrule mesostases in the co chondrites of higher subtypes 3 2 3 7 contain various amounts of nepheline in addition to glass and plagioclase nepheline has replaced glass and plagioclase forming finegrained aggregates and thin parallel lamellar intergrowths with plagioclase the nephelinization has proceeded preferentially from the outer margins of chondrules toward the inside although the degree of nephelinization differs widely among chondrules in each of the metamorphosed chondrites our modal analyses and bulk chemical analyses of individual mesostases indicate that the amounts of nepheline in chondrules systematically increase with the increasing petrologic subtype of the host chondrites nepheline also has a tendency to increase in grain size with increasing petrologic subtype we conclude that nepheline in chondrules in the co3 chondrites has formed largely as a result of effects related to heating on the meteorite parent body we suggest that nepheline initially formed as hydrous nepheline under the presence of aqueous fluids and subsequently was dehydrated after exhaustion of aqueous fluids the degree of hydrothermal activity must have increased with increasing degree of heating and thus chondrules in more thermally metamorphosed chondrites produced larger amounts of nepheline the results imply that co3 chondrites have gone through lowgrade aqueous alteration and subsequent dehydration at the early stage of heating on the meteorite parent body

petrology of allende dark inclusions abstract bulk compositions acquired by neutron activation analysis are reported for eight allende dark inclusions dis and compared with compositions of five dis previously reported in the literature enrichments of the elements na k br ba au and as are generally correlated with increased proportions of porous aggregates predominantly composed of fine grained platy to fibrous olivine these aggregates have been interpreted by some workers as chondrules and inclusions that first were exposed to aqueous alteration converting anhydrous silicates to phyllosilicates and later were dehydrated by thermal metamorphism converting phyllosilicates to olivine our data support this interpretation and suggest that the aqueous alteration was open system in character feldspathoid grains intergrown with platy to fibrous olivines in porous olivine rich aggregates and inclusions of sodalite nepheline pentlandite ilmenite and spinel in these olivines suggest that phyllosilicates produced during aqueous alteration could accommodate na k ni s etc and are most consistent with a mixture of both saponite and serpentine dehydration of saponite would require that the temperature of thermal metamorphism was higher than previously suggested and may have been as high as 800 900 c nonporous rims containing ca rich minerals andradite hedenbergite surrounding dark inclusions containing highest proportions of porous olivine rich aggregates and slight to moderate depletions of these clasts in ca relative to bulk allende suggest that these rims were also the result of redistribution of some elements during dehydration of these clasts caused by thermal metamorphism

oxygen silicon and mn cr isotopes of fayalite in the kaba oxidized cv3 chondrite constraints for its formation history the iron rich olivine end member fayalite occurs in the matrix chondrules ca al rich inclusions cais silicate aggregates and dark inclusions in the kaba and mokoia oxidized cv3 chondrites in most occurrences fayalite is associated with magnetite and troilite to help constrain the origin of the fayalite fa98 100 we measured oxygen and silicon isotopic compositions and mn cr systematics in fayalite from two petrographic settings of the kaba meteorite one setting consists of big fayalite laths embedded in the matrix and radiating from a core of fine grained magnetite and sulfide while the other setting consists of small fayalite magnetite sulfide assemblages within or at the surface of type i barred or porphyritic olivine chondrules oxygen in the big fayalite laths and small chondrule fayalites falls on the terrestrial fractionation line and is distinct from that in chondrule forsterites which are enriched in 16o 17o 4 oxygen in the big fayalite laths may be isotopically heavier than that in chondrule fayalites silicon isotopes suggest that forsterite is 1 amu heavier than adjacent fayalite within kaba chondrules however we were unable to confirm large silicon isotopic differences among fayalites reported previously the mn cr data for big kaba fayalites give an initial 53mn 55mn ratio of 2 07 0 17 10 6 consistent with literature results on mokoia chondrule fayalites the combined data suggest that fayalites in both petrographic settings formed at about the same time 9 7 ma after the formation of cais our data indicate that those fayalite magnetite troilite assemblages replacing metal inside and around chondrules formed by aqueous alteration on the meteorite parent body the formation site and mechanism for the big fayalite laths is less clear but the petrographic setting indicates that they did not form in situ none of the models that have been suggested for formation of these fayalites is entirely satisfactory

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

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

multiple melting in a four layered barred olivine chondrule with compositionally heterogeneous glass from ll3 0 semarkona chondrule k7p from ll3 0 semarkona consists of four nested barred olivine bo chondrules the innermost bo chondrule chondrule 1 formed by complete melting of an olivine rich dustball after formation the chondrule was incorporated into another olivine rich dustball a second heating event caused this second dustball to melt the mesostasis and some of the olivine in chondrule 1 were probably also melted at this time but the chondrule 1 structure remained largely intact at this stage the object was an enveloping compound bo chondrule this two step process of melting and dustball enshrouding repeated two more times the different proportions of olivine and glass in chondrules 1 4 suggest that the individual precursor dustballs differed in the amounts of chondrule fragments they contained and the mineral proportions in those fragments the final dustball which ultimately formed chondrule 4 was somewhat more ferroan after melting crystallizing and quenching chondrule 4 contained olivine and glass with higher feo and mno contents than those of the earlier formed chondrules subsequent aqueous alteration on the ll parent body transformed the abundant metal blebs and stringers at the chondrule surface into carbide iron oxide and minor ni rich metal portions of the mesostasis underwent dissolution producing holes and adjacent blades of more resistant material much of the glass in the chondrule remained isotropic even after minor hydration and leaching the sharp moderately lobate boundary between the extensively altered mesostasis and the isotropic glass represents the reaction front beyond which there was little or no glass dissolution

the leoville cv3 accretionary breccia leoville is a cv3 chondrite that contains a large variety of inclusions besides refractory inclusions resembling those in allende fine grained dark inclusions are especially prominent same of these are xenoliths of material very similar to cm chondrites in texture bulk composition and oxygen isotopes however they show an unusually large range in the degree of hydrous alteration other dark inclusions are similar to host matrix the cv3 host of this breccia is similar to other cv chondrites although less metamorphosed than allende we suggest that leoville is a typical accretionary breccia whose parent body accreted after the cm like material represented by the xenoliths had formed and undergone alteration after accretion leoville suffered severe deformation leading to foliation stronger than in any other chondrite but the nature of the event that caused this remains unclear

53mn 53cr dating of fayalite formation in the cv3 chondrite mokoia evidence for asteroidal alteration fayalite grains in chondrules in the oxidized aqueously altered cv3 chondrite mokoia have large excesses of radiogenic chromium 53 these excesses indicate the in situ decay of short lived manganese 53 half life 3 7 million years and define an initial53mn 55mn ratio of 2 32 0 18 10 6 this ratio is comparable to values for carbonates in ci and cm chondrites and for several classes of differentiated meteorites mokoia fayalites formed 7 to 16 million years after allende calcium aluminum rich inclusions during hydrothermal activity on a geologically active asteroid after chondritic components had ceased forming in the solar nebula

nepheline and sodalite in chondrules of the ningqiang carbonaceous chondrite implications for a genetic relationship with those in the matrix abstract ningqiang is an ungrouped carbonaceous chondrite that has a chemical and mineralogical affinity to cv3 chondrites the ningqiang matrix has distinctly higher abundances of na k and al than cv3 matrices a recent study by matsumoto et al 2014 revealed that the major proportions of these elements can be attributed to the presence of nepheline and sodalite scanning electron microscopy revealed that all of the ningqiang chondrules studied show abundant evidence of extensive na fe metasomatism only a small proportion of the chondrules contain primary mesostases in their cores but the mesostases in their mantles were replaced by fine grains of nepheline sodalite fe rich olivine and hedenbergite the mesostases in the majority of the chondrules were completely replaced by fine grains of the same secondary minerals most opaque nodules were also largely replaced by various fine grained secondary minerals nepheline sodalite form veins penetrating the primary mesostases providing evidence that aqueous fluids were involved in the alteration reactions the nepheline sodalite in the mesostases contain various amounts of inclusions of fe rich olivine diopside hedenbergite fe sulfides and magnetite the mineralogical features of the nepheline sodalite in the mesostases are almost identical to those in the meteorite matrix these results suggest that a significant fraction of the nepheline sodalite grains in the ningqiang matrix originated from the nepheline sodalite produced in chondrules and refractory inclusions and that they were disaggregated and mixed into the matrix these processes can be explained consistently by the model of the dynamic formation of chondrite lithology in a parent body proposed by tomeoka and ohnishi 2015 we suggest that after a ningqiang precursor with a cv3 like lithology was metasomatized it was fragmented causing the disaggregation of the fine grained host matrix and the fine grained altered mesostases including nepheline sodalite and opaque nodules in the chondrules the chondrules were thereby separated into multiple fragments subsequently during transportation in a fluidized state all these materials were homogenously mixed together and later underwent accumulation and lithification

the i xe record of alteration in the allende cv chondrite abstract complex i xe and mineralogical studies have been performed on four heavily altered allende fine grained spinel rich ca al rich inclusions cais and four allende dark inclusions dis showing various degrees of iron alkali metasomatic alteration the cais are largely composed of fe rich spinel al diopside and secondary nepheline and sodalite the dis consist of chondrules and allende like matrix composed of lath shaped fayalitic olivine nepheline sodalite and ca fe rich pyroxene andradite feni sulfide nodules chondrule phenocrysts are extensively or completely replaced by fayalitic olivine nepheline and sodalite metal nodules are replaced by feni sulfides andradite and ca fe rich pyroxenes the chondrules and matrices are crosscut by ca fe rich pyroxene feni sulfide fayalitic olivine veins dis are surrounded by continuous ca rich rims composed of andradite wollastonite kirschsteinite and ca fe rich pyroxenes whereas the outer portions of the inclusions are depleted in ca three cais yield well defined i xe isochrons with ages 3 1 0 2 3 0 0 2 and 3 7 0 2 ma younger than the shallowater internal standard 4566 2 ma similar release profiles suggest the same iodine carrier most probably sodalite for all four cais the allende dis yield i xe ages from 0 8 0 3 to 1 9 0 2 ma older than shallowater based on the petrographic observations we infer that the dis experienced at least two stage alteration during an early stage of the alteration which took place in an asteroidal setting but not in the current location of the dis chondrule silicates were replaced by secondary fayalitic olivine nepheline and sodalite calcium lost from the chondrules was redeposited as ca fe rich pyroxene veins and ca fe rich pyroxene andradite nodules in the matrix the second stage of alteration resulted in mobilization of ca from the dis and its re deposition as ca rich rims composed of ca fe rich pyroxenes andradite and wollastonite around the dis we interpret i xe ages of the dis as time of their alteration prior incorporation into allende the younger i xe ages of the fine grained spinel rich cais may reflect hydrothermal alteration of the allende host which could have occurred contemporaneously with the second stage of alteration of the allende dis the lack of evidence for the disturbance of i xe system in the allende dis may suggest that fluid responsible for the alteration of the allende cais was in equilibrium with the i and xe bearing phases of the dis