reduction during metamorphism of four ordinary chondrites abstract three type 3 chondrite finds willaroy suwahib buwah and moorabie and one type 4 find cerro los calvos are ordinary chondrites oc in all respects except redox state a they have oc abundances of refractory lithophiles cerro los calvos data are ambiguous zn and other taxonomic elements b they have oc matrix chondrule abundance ratios and their chondrule sizes are consistent with bulk siderophile indicators of group membership h for willaroy and cerro los calvos l for suwahib buwah and moorabie and c their oxygen isotope compositions are far closer to those of oc than to those of any other chondrite group in each of the four chondrites the range of olivine compositions is relatively narrow fayalite modes and means are distinctly below those of other members of their respective groups having similar or greater degrees of equilibration the most plausible explanation of these properties is that these four oc experienced reduction during metamorphism this is consistent with reverse zoning in olivine from one type ii chondrule in willaroy the reducing agents may have been foreign clasts incorporated during an earlier accretional history alternatively these chondrites could themselves have been foreign materials incorporated into a reduced regolith examples of reducing clasts are the c rich aggregates in sharps examples of reducing host regoliths are the host materials in bencubbin and cumberland falls confirmation of this interpretation will require identification of the reduced foreign material or their relicts in the four reduced oc initial searches have been unsuccessful

the fine grained matrix of the semarkona ll3 0 ordinary chondrite an induced thermoluminescence study to investigate the nature origin and history of the fine grained matrix in semarkona and develop techniques suitable for small samples we have measured the induced thermoluminescence properties of six matrix samples 10 m to 400 m in size the samples had tl sensitivities comparable with 4 mg of bulk samples of type 3 2 3 4 ordinary chondrites which is very high relative to bulk semarkona the other induced tl properties of these samples tl peak temperatures and tl peak widths distinguish them from other ordinary chondrite samples where the tl is caused by feldspar cathodoluminescence images and other data suggest that the cause of the luminescence in the semarkona fine grained matrix is forsterite in some respects the matrix tl data resemble that of semarkona chondrules in which the phosphor is forsterite and terrestrial forsterites from a variety of igneous and metamorphic environments however differences in the tl peak temperature versus tl peak width relationship between the matrix samples and the other forsterites suggest a fundamentally different formation mechanism we also note that forsterite appears to be a major component in many primitive materials such as nebulae cometary dust and stardust particles

187re 187os systematics highly siderophile element s se te abundances in the components of unequilibrated l chondrites abstract the 187re 187os systematics abundances of highly siderophile elements hse re platinum group elements and au te se and s as well as major and minor elements were determined in separated components of two unequilibrated l chondrites que 97008 l3 05 and ceniceros l3 7 the 187re 187os systematics are disturbed in the components of both meteorites most likely due to open system behavior of re during terrestrial weathering of que 97008 and alteration on the l chondrite parent body as indicated by an internal errorchron generated for components of ceniceros the hse abundance patterns suggest that the bulk rock abundances were mainly controlled by two different end members non magnetic fractions display lower re os and hse ir than ci chondrites chondrules metal troilite spherules and fine magnetic fractions are depleted in refractory hse and show higher rh ir pd ir and au ir than in ci chondrites the different hse compositions indicate the presence of unequilibrated alloys and loss of refractory hse rich carrier phases from the precursors of some l chondrite components gold is decoupled from other hse in magnetic fractions and shows chalcophile affinities with a grain size dependent variation similar to s and se presumably inherited from preaccretionary processes tellurium is depleted in all components compared to other analysed siderophile elements and its abundance was most likely controlled by fractional condensation and different geochemical affinities the volatility dependent depletion of te requires different physical and chemical conditions than typical for the canonical condensation sequence as represented by carbonaceous chondrites tellurium also shows variable geochemical behavior siderophile in ceniceros predominantly chalcophile in que 97008 these differences may have been inherited from element partitioning during chondrule formation selenium and s on the other hand are almost unfractionated from each other and only show complementary s se in a few components presumably due to the effects of volatility or metal silicate partitioning during chondrule formation terrestrial weathering had negligible effects on the s se and te systematics

oxygen isotopic heterogeneities their petrological correlations and implications for melt origins of chondrules in unequilibrated ordinary chondrites abstract ten whole chondrules separated from the dhajala h3 4 hallingeberg l3 and semarkona ll3 chondrites were individually analyzed for bulk element composition by instrumental neutron activation with half of each chondrule subsequently sacrificed for oxygen isotopic analysis and half retained for petrographic and electron microprobe analysis on a three isotope plot 17 o vs 18 o the chondrules neither cluster near their respective chondrite hosts nor in the vicinities of previously recognized chondrite group averages instead they define a trend resolvable into mixing and fractionation components but dominated by mixing in a manner similar to that previously observed for clasts from the ll3 chondrite alha76004 covariations of chondrule isotopic mixing and fractionation parameters with petrological parameters were sought by two variable linear least squares regression analyses however the only two isotopic petrological correlations significant at the 95 confidence level were 17 o vs total bulk fe r 0 68 and mixing parameter m 18 vs bulk weight ratio cao al 2 o 3 mgo r 0 67 other correlations of apparent statistical significance were found by treating the chondrules as separate porphyritic 3 porphyritic olivine pyroxene 1 porphyritic olivine 1 barred olivine and non porphyritic 4 radial pyroxene 1 granular pyroxene cryptocrystalline textural subgroups the reliability of the trends based on so few samples is not clear but the results at least indicate that possible existence of distinct isotopic petrological subgroups of chondrules should be further investigated absence of certain isotopic petrological trends expected as condensation effects argues against direct nebular condensation as the dominant process of chondrule formation instead a model involving melting of heterogeneous solids followed by various degrees of liquid gas exchange is favored in any case chondrule oxygen isotopic evolution was dominated by two component mixing fractional vaporization was at most a second order effect in addition to chondrules parent bodies of unequilibrated ordinary chondrites must have also incorporated a 16 o rich component which might have been fine grained matrix

microchondrules in three unequilibrated ordinary chondrites we report on a suite of microchondrules from three unequilibrated ordinary chondrites uocs microchondrules a subset of chondrules that are ubiquitous components of uocs commonly occur in fine grained chondrule rims although may also occur within matrix microchondrules have a variety of textures cryptocrystalline microporphyritic radial glassy in some cases their textures and in many cases their compositions are similar to their larger host chondrules bulk compositions for both chondrule populations frequently overlap the primary material that composes many of the microchondrules has compositions that are pyroxene normative and is similar to low ca pyroxene phenocrysts from host chondrules primary material rarely resembles olivine or plagioclase some microchondrules are composed of feo rich material that has compositions similar to the bulk submicron fine grained rim material these microchondrules however are not a common compositional type and probably represent secondary feo enrichment microchondrules may also be porous suggestive of degasing to form vesicles our work shows that the occurrence of microchondrules in chondrule rims is an important constraint that needs to be considered when evaluating chondrule forming mechanisms we propose that microchondrules represent melted portions of the chondrule surfaces and or the melt products of coagulated dust in the immediate vicinity of the larger chondrules we suggest that through recycling events the outer surfaces of chondrules were heated enough to allow microchondrules to bud off as protuberances and become entrained in the surrounding dusty environment as chondrules were accreting fine grained rims microchondrules are thus byproducts of cyclic processing of chondrules in localized environments their occurrence in fine grained rims represents a snapshot of the chondrule forming environment we evaluate mechanisms for microchondrule formation and hypothesize a potential link between the emergence of type ii chondrules in the early solar system and the microchondrule bearing fine grained rims surrounding type i chondrules

refractory precursor components of semarkona chondrules and the fractionation of refractory elements among chondrites abstract chondrules from the semarkona ll3 0 chondrite show refractory and common lithophile fractionation trends similar to those observed among the chondrite groups it appears that chondrules are mixtures of a small number of pre existing solid components and we infer that chondrule precursor materials were related to the nebular components involved in the lithophile element fractionations recognized in ordinary chondrites compositional trends among the chondrules can be used to deduce the compositions of these components we use instrumental neutron activation analysis to measure many 20 of the lithophile elements in 30 chondrules the amounts of oxidized iron were calculated from other compositional parameters concentrations of si were estimated using mass balance considerations the data were corrected for the diluting effects of non lithophile constituents plots of lithophile elements versus a reference refractory element such as al show that there were two major chondrule silicate precursor components a refractory olivine rich feo free one and a non refractory sio 2 feo rich one the refractory component probably forms from olivine enriched condensates formed above the condensation temperature of enstatite the non refractory component must have formed from fine grained materials that were able to equilibrate down to lower nebular temperatures chondrite matrix may have had an origin similar to that of the non refractory material and constitutes a third lithophile bearing component that took part in chondrite fractionation processes the low abundance of refractories and mg in ordinary and enstatite chondrites was produced by the loss of materials having a higher refractory element mg ratio than that in the refractory component of chondrules

origin of chondrule rims and interchondrule matrices in unequilibrated ordinary chondrites optical microscopy electron probe microanalysis scanning electron microscopy and analytical transmission electron microscopy were used to study the interchondrule matrix and opaque chondrule rims in bishunpur krymka semarkona chainpur all ll3 tieschitz and sharps both h3 the size distribution of grains in matrix in bishunpur obeys a power law rims around chondrules tend to be finer grained than matrix and may be layered all rims and matrices studied contain clasts of forsteritic olivine and low ca pyroxene in bishunpur the clasts may be cemented by amorphous glue rich in normative albite and partly altered to smectite rims in krymka sharps chainpur and tieschitz have a densely packed olivine groundmass with a grain size of about 0 1 m in krymka groundmass olivine is fo20 30 and forms interlocking dendrites various fe oxides are present in rims and matrices grain size distribution and chemical data indicate that clastic olivines and pyroxenes are derived from chondrules from analyses matrices rims in the ll group apparently are enriched in a feldspathic component tieschitz rims are slightly enriched but here the feldspathic component is present as white matrix sharps rims are not enriched in a feldspathic component opaque interchondrule matrices and chondrule rims probably formed from the products of fragmentation of chondrules partly induced by contraction of protopyroxene on inversion to clinopyroxene fragmented silica rich chondrule mesostases reacted with fe oxides and na to form the groundmass of fayalitic olivine and feldspathic glue a low temperature nebular or pre solar component is limited to 3 vol of each meteorite so equilibrium condensate was not the carrier of volatiles such as tl and bi

shock and annealing in aubrites implications for parent body history several aubrites e g lap 03719 bishopville khor temiki alh 83015 contain orthopyroxene grains that exhibit more pronounced shock effects than associated olivine grains the orthopyroxene grains in these samples have clinoenstatite lamellae on 100 and exhibit weak mosaic extinction characteristic of shock stage s4 the olivine grains exhibit either sharp optical extinction characteristic of shock stage s1 as in lap 03719 or undulose extinction shock stage s2 as in bishopville and alh 83015 the khor temiki regolith breccia contains s1 and s2 olivine grains because literature data show that diffusion is much slower in orthopyroxene than in olivine it seems likely that aubrites experienced postshock impact induced annealing after differentiation the aubrite parent asteroid suffered major collisions that caused extensive brecciation of near surface materials and damaged orthopyroxene and olivine crystal lattices as a result of these impact events some aubrites were shocked and buried within warm ejecta blankets or beneath fallback debris under the crater floor entombed olivine crystal lattices healed and became unstrained reaching shock stage s1 but orthopyroxene lattices retained their s4 level shock damaged features aubrites with s4 orthopyroxene and s2 olivine were probably very weakly shocked again after olivine was annealed to s1

chemical and physical studies of type 3 chondrites ix thermoluminescence and hydrothermal annealing experiments and their relationship to metamorphism and aqueous alteration in type 3 3 ordinary chondrites samples of four type 3 chondrites have been annealed at 400 850 c and 0 77 1 kbar for 10 500 h in the presence of various amounts of water 0 10 wt and sodium disilicate 0 2 molal and their thermoluminescence properties measured after annealing for 20 h at temperatures 600 c the tl sensitivity of the samples increased by factors of up to 40 after annealing at 800 c when both high and low forms were present originally the low form was destroyed preferentially we suggest that these data are consistent with the tl metamorphism trends observed in type 3 2 chondrites being due to the formation of feldspar with structural details being dependent on formation temperature by the devitrification of chondrule glass during metamorphism for types 3 2 the tl data are equally consistent with these types experiencing lower levels of metamorphism than the higher types or with type 3 0 being produced from higher types by aqueous alteration the presence of water with non terrestrial d h ratios and petrographic evidence for aqueous alteration in semarkona lead us to favour the aqueous alteration hypothesis

chondrules in the sharps h3 chondrite evidence for intergroup compositional differences among ordinary chondrite chondrules abstract bulk compositions of 19 chondrules and one matrix rich sample from h3 4 sharps were determined by instrumental neutron activation analysis samples were characterized petrographically and mineral compositions were determined by electron microprobe analysis there is constancy among ordinary chondrite oc groups in the compositional interrelationships of different chondrule types e g in h3 as well as l3 and ll3 chondrites porphyritic chondrules are more refractory than nonporphyritic chondrules precursor components of h3 chondrules are closely related to those of ll3 chondrules the mean ir ni ir co and ir au ratios of h3 chondrules differ from the corresponding ratios of ll3 chondrules at the 99 90 and 79 confidence levels respectively the ratios in h3 chondrules exceed those in ll3 chondrules by amounts similar to those by which h whole rocks exceed ll whole rocks these data suggest that there are primary systematic differences in bulk composition between h and ll chondrules these differences support the inference that chondrule formation occurred after major nebular fractionation events had established the observed bulk compositional differences among oc groups

highly siderophile element and osmium isotope evidence for postcore formation magmatic and impact processes on the aubrite parent body abstract aubrites exhibit a wide range of highly siderophile element hse re os ir ru rh pt pd au concentrations and 187os 188os compositions their hse concentrations are one to three orders of magnitude less than chondrites with the exception of the shallowater and mt egerton samples while most aubrites show chondritic hse abundance ratios significant enrichments of pd and re relative to os ir and ru are observed in 12 of 16 samples present day 187os 188os ratios range from subchondritic values of 0 1174 to superchondritic values of up to 0 2263 half of the samples have 187os 188os ratios of 0 127 to 0 130 which is in the range of enstatite chondrites along with the brecciated nature of aubrites the hse and re os isotope systematics support a history of extensive postaccretion processing including core formation late addition of chondritic material and or core material and potential breakup and reassembly highly siderophile element signatures for some aubrites are consistent with a mixing of hse rich chondritic fragments with a hse free aubrite matrix the enrichments in incompatible hse such as pd and re observed in some aubrites reminiscent of terrestrial basalts suggest an extensive magmatic and impact history which is supported by both the 187re 187os isotope system and silicate hosted isotope systems rb sr k ar yielding young formation ages of 1 3 3 9 ga for a subset of samples compared with other differentiated achondrites derived from small planetary bodies aubrites show a wide range in hse concentrations and 187os 188os most similar to angrites while similarities exist between the diverse groups of achondrites formed early in solar system history the aubrite parent body ies clearly underwent a distinct evolution different from angrites brachinites ureilites howardites eucrites and diogenites

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

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

mineralogy of fine grained material in the krymka ll3 1 chondrite two dark lithic fragments and matrix of the krymka ll3 1 chondrite were mineralogically and chemically studied in detail these objects are characterised by the following chemical and mineralogical characteristics which distinguish them from the host chondrite krymka 1 bulk chemical analyses revealed low totals systematically lower than 94 wt due to high porosity 2 enrichment in feo and depletion in s mgo and sio2 due to a high abundance of fe rich silicates and low sulfide abundance 3 fine grained almost chondrule free texture with predominance of a porous cryptocrystalline groundmass and fine grains 4 occurrence of a small amount of once molten material microchondrules enclosed in fine grained materials 5 occurrence of accretionary features especially unique accretionary spherules 6 high abundance of small calcium aluminium rich inclusions cais in one of the fine grained fragments it is suggested that the abundance of cais in this fragment is one of the highest ever found in an ordinary chondrite accretionary fine grained spherules within one of the fragments bear fundamental information about the initial stages of accretion as well as on the evolution of the clast its incorporation and history within the bulk rock of krymka the differences in porosity bulk composition and mineralogy of cores and rims of the fine grained spherulitic objects allow us to speculate on the following processes 1 low velocity accretion of tiny silicate grains onto the surface of coarse metal or silicate grains in a dusty region of the nebula is the beginning of the formation of accretionary porous fluffy silicate spherules 2 within a dusty environment with decreasing silicate metal sulfide ratio the porous spherules collected abundant metal and sulfide particles together with silicate dust which formed an accretionary rim variations of the silicate sulfide metal ratio in the dusty nebular environment result in the formation of multi layered rims on the surface of the silicate rich spherules 3 soft accretion and lithification of rimmed fluffy spherules fine grained silicate rich dust metal sulfide particles cais silicate rich microchondrules and coarse silicate grains and fragments followed 4 after low temperature processing of the primary accretionary rock collisional fragmentation occurred the fragments were subsequently coated by fine grained material which was highly oxidized and depleted in sulfides 5 in a final stage this accretionary dusty rock was incorporated as a fragment within the krymka host

microstructural analysis of wark lovering rims in the allende and axtell cv3 chondrites implications for high temperature nebular processes a coordinated electron backscatter diffraction ebsd and transmission electron microscope tem study was undertaken to obtain information on the origin of rims on refractory inclusions in the allende and axtell cv3 chondrites these measurements were supported by theoretical modeling using density functional theory crystal orientation analysis of wark lovering rims via ebsd revealed pyroxene grains with similar crystallographic orientations to one another in both inclusions an epitaxial relationship between grains within the diopside and anorthite rim layers was observed in allende tem examination of the rims of both samples also revealed oriented crystals at depth the microstructural data on the rims suggest that grain clusters grew in the form of three dimensional islands density functional theory calculations confirm that formation of oriented grain islands is the result of energy minimization at high temperature the results point toward condensation as the mode of origin for the rims studied here

the thermal release of hg from chondrites and their thermal histories a quantitative treatment and implications of isothermal and linear heating data on hg in meteorites are given as a sequel to a more qualitative analysis of meteorite thermal histories reed and jovanovic 1968 studies of hg in terrestrial metamorphic rocks establish that thermal events to which meteorites were subjected fall in the same temperature range 400 900 c as exists during terrestrial metamorphism hg diffusion parameters based on data from the linear and isothermal heating experiments are calculated the conclusions are 1 1 meteorites experienced thermal events of the same magnitude as those measured by primarily mineralogical metamorphic indicators reviewed by dodd 1969 2 2 no correspondence with mineralogical petrological metamorphic grade is evident 3 3 hg data for some chondrites correlate with shock facies non thermal indicators dodd and jarosewich 1979 4 4 small hg activation energies 6 14 kcal mole require that the meteorites must have been stored in closed systems until low temperatures were attained hg must be present as an involatile mineral s or as a substituent in a host phase at temperatures below 100 c consistent with this interpretation is the fact that despite diffusion times of 102 106 years at 200 k hg was retained in small objects over cosmic ray exposure periods of 107 years

morphological impacts of the chilean megathrust earthquake mw 8 8 on coastal wetlands of high conservation value abstract the subduction earthquake mw 8 8 on february 27th 2010 which affected chile s south central coast 37 s produced a co seismic uplift of 1 4 m in coastal tubul raqui wetland area with abrupt morphological changes in order to determine the magnitude of the changes in this area of high conservation value salt marsh morphological features were identified and quantified by mapping the changing extent of the coverage of morphological features before 2009 and after 2011 2012 the tectonic disturbance rectified satellite images of seven study sites were created for the three years using google earth images and processed in arcgis the results indicate a total decline of 31 7 in the area of the morphological features and the emergence of 1 25 km2 of dried area salt pans and tidal creeks were severely affected with more than 90 loss in contrast there was a slight recovery of the tubul and raqui main river channel 12 and the tidal channels 8 5 between 2011 and 2012 mainly in the area near the river mouth the salt marsh cover by spartina densiflora showed slight variation after the co seismic uplift 14 6 demonstrating high tolerance in the face of high impact natural disturbances the changes and later evolution may be explained mostly by the action of the seismic cycle in subduction zones continuing to monitor state of the recovery of the salt marsh and other similar environments may help to understand the true role that the seismic cycle plays in the dynamics of coastal ecosystems as well as its incidence in the recovery process

recovery estimates for the rio cruces after the may 1960 chilean earthquake abstract the may 22nd 1960 chilean earthquake was the largest earthquake on record with a magnitude 9 5 the event caused extensive subsidence and uplift over wide areas at least 130 000 km 2 with uplift on the offshore south american plate margin and downwarping in the coastal and landward areas which ranged in magnitude from 1 2 m the subsidence deepened coastal rivers creating extensive shallow banks now wetlands in many rivers including the rio cruces the amount of subsidence was well documented with field measurements recorded soon after the event this study using sediment accumulation histories predicts the recovery time of the rio cruces to pre 1960 conditions an important factor for assessing the fidelity of seismic recorders in the geological record sediment cores n 139 from the subtidal areas of the rio cruces were lithologically logged and selectively analyzed using high resolution particle size distribution psd plots microfossil analysis thecamoebians and 210 pb 137 cs dating documenting the post 1960 thickness of sediment the analysis differentiated four main facies which include 1 floodplain soil horizon 2 tsunami or flood unit 3 post earthquake adjustment and 4 river sedimentation the post 1960 river sediment is clearly demarcated in the cores by highly peaked psds 4 5 phi abundant thecamoebian tests and high diversities compared to the underlying facies species compositions are typical of lacustrine or slow moving river systems cucurbitella tricuspis difflugia oblonga centropyxis constricta centropyxis aculeata lagenodifflugia vas and difflugia protaeiformis based on this core data the shallow banks along the rio cruces will likely shoal in less than 100 yrs

cumberland falls chondritic inclusions iii consortium study of relationship to inclusions in allan hills 78113 aubrite abstract we describe the mineralogy and report contents of ag au bi cd co cs ga in rb sb se te tl u and zn determined by rnaa in three primitive chondritic inclusions from the alh a78113 aubrite comparison of these data with those for large petrologic type 3 chondritic clasts from the cumberland falls aubrite and the discovery of small clasts in it like those in alh a78113 indicate that all constitute a single chondritic suite we also report thermoluminescence data for cumberland falls chondritic inclusions and achondritic host these results together with mineralogie major minor and trace element information demonstrate that aubrite inclusions represent a different sort of type 3 chondrite not an ll3 chondrite altered during equilibration with aubrite host instead the aubrite inclusions represent a distinct chondrite class these inclusions reflect nebular condensation accretion over a broad redox range and at temperatures relatively high compared with those at which other type 3 chondrites formed limited metamorphism and reduction occurred during condensation accretion prior to incorporation into aubrite host during the impact of the chondritic parent body with the aubrite parent body chondrite fragments were strongly shocked and cooled rapidly they then mixed with aubrite host possibly in a regolith so that these aubrites now represent impact breccias

thermoluminescence and compositional zoning in the mesostasis of a semarkona group a1 chondrule and new insights into the chondrule forming process a large group a1 porphyritic olivine chondrule in the semarkona ll3 0 chondrite with induced thermoluminescence tl and compositional zoning in its mesostasis has been discovered the chondrule has ca rich and fe poor olivine cao 0 36 0 40 wt fa0 3 0 5 and its mesostasis is highly anorthite normative 52 5 wt the chondrule shows an intense induced tl peak at 300 c with a half width of 180 c the induced tl in the 40 440 c range increases monotonically by a factor of 6 from center to rim while sio2 na2o and mno increase by factors of 1 1 3 6 and 6 respectively the spectrum of the induced tl over the 200 350 c range i e a dominant peak at 570 nm with a half width of about 100 nm and the mn tl correlation suggest mn activated plagioclase is an important constituent of the refractory mesostases in group a1 chondrules the zoning may reflect fractional crystallization soret diffusion transport of volatiles into the chondrule by aqueous alteration a zoned precursor reduction of precursor dust aggregate or recondensation of volatiles lost during chondrule formation the first four possibilities seem unlikely explanations for the zoning of the mesostasis but both reduction of precursor dust aggregate and recondensation of volatiles seem to have played significant roles to the formation of the zoning reducing conditions at high temperatures are suggested to have prevailed during the formation of group a1 chondrules

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

26al 26mg deficit dating ultramafic meteorites and silicate planetesimal differentiation in the early solar system abstract meteorites with significantly sub chondritic al mg that formed in the first 2 million years of the solar system should be characterised by deficits in the abundance of 26mg 26mg due to the absence of in growth of 26mg from the decay of short lived 26al t1 2 0 73 myr however these 26mg deficits will be small 26mg 0 037 even for material that formed at the same time as the solar system s oldest solids calcium aluminium rich inclusions and thus measurement of these deficits is analytically challenging here we report on a search for 26mg deficits in three types of ultramafic meteorites pallasites ureilites and aubrites by multiple collector inductively coupled plasma mass spectrometry a range of analytical tests were carried out including analysis of 1 a range of synthetic mg solution standards 2 mg gravimetrically doped with a high purity 26mg spike 3 mg cuts collected sequentially from cation exchange separation columns with fractionated stable mg isotope compositions 4 mg separated from samples that was bracketed by analyses of both dsm 3 and mg separated from a natural olivine sample subjected to the same chemical processing as the samples these tests confirm it is possible to resolve differences in 26mg from the terrestrial materials that are 0 005 however if mg yields from chemical separation are low or an inappropriate equilibrium isotopically fractionated standard is used this will generate analytical artefacts on 26mg when this is calculated with the kinetic exponential mass fractionation law as is the case when correcting for instrumental mass bias during mass spectrometric analysis olivine from four different main group pallasites and four bulk ureilites have small deficits in the abundance of 26mg with 26 mg dsm 3 0 0120 0 0018 and 26 mg dsm 3 0 0062 0 0023 respectively relative to terrestrial olivine 26 mg dsm 3 0 0029 0 0028 six aubrites have 26 mg dsm 3 0 0015 0 0020 which is identical to terrestrial olivine model ages from these deficits can be calculated by assuming that 26al was homogeneously distributed in the planetesimal forming regions of the proto planetary disc at the same level as calcium aluminium rich inclusions cais the absence of 26mg deficits in aubrites means these can only be constrained to have formed relatively late 2 9 myr after cai formation model ages calculated from pallasite olivine deficits would suggest that pallasite olivine crystallised and was diffusively isolated on its parent body 1 24 0 28 0 40 myr after formation of cais similarly ureilites would have experienced silicate partial melting and lowering of their bulk al mg ratios 1 9 0 7 2 2 myr after cai formation the model ages for silicate differentiation on the main group pallasite parent body are intermediate between those for metal silicate fractionation for core formation obtained from magmatic iron meteorites and those for asteroidal silicate magmatism obtained from basaltic meteorites

quantified whole section trace element mapping of carbonaceous chondrites by synchrotron x ray fluorescence microscopy 1 cv meteorites abstract we present the application of a new synchrotron based technique for rapid mapping of trace element distributions across large areas of the cv3 meteorites allende and vigarano this technique utilizes the australian synchrotron x ray fluorescence microscopy xfm beam line with its custom designed and built x ray detector array called maia xfm with maia allows data to be collected using a 2 m spot size at very low dwell times 0 1 0 5 ms resulting in maps of entire thin sections in 5 h maia is an energy dispersive detector system with a large collection solid angle which allows full spectral acquisition and high sensitivity hence there is no need to constrain the elements of interest a priori we collected whole section maps 2 cm 1 cm from 3 thick sections of allende and a single map 2 cm 1 5 cm from a thick section of vigarano our experimental conditions provide data for elements with 20 z 40 k shell ca through zr and the l emissions of os ir pt au and pb we illustrate the unique capabilities of this technique by presenting observations across myriad length scales from the centimeter scale down to the detection of sub micrometer particles within these objects our initial results show the potential of this technique to help decipher spatial and textural variations in trace element chemistry between cais chondrules matrix and other chondritic components we also illustrate how these datasets can be applied to understanding both nebular and parent body processes within meteorites

revealing the deep structure and rupture plane of the 2010 maule chile earthquake mw 8 8 using wide angle seismic data the 27 february 2010 maule earthquake mw 8 8 ruptured 400 km of the nazca south america plate boundary and caused hundreds of fatalities and billions of dollars in material losses here we present constraints on the fore arc structure and subduction zone of the rupture area derived from seismic refraction and wide angle data the results show a wedge shaped body 40 km wide with typical sedimentary velocities interpreted as a frontal accretionary prism fap landward of the imaged fap the velocity model shows an abrupt velocity contrast suggesting a lithological change which is interpreted as the contact between the fap and the paleo accretionary prism backstop the backstop location is coincident with the seaward limit of the aftershocks defining the updip limit of the co seismic rupture and seismogenic zone furthermore the seaward limit of the aftershocks coincides with the location of the shelf break in the entire earthquake rupture area 33 s 38 5 s which is interpreted as the location of the backstop along the margin published seismic profiles at the northern and southern limit of the rupture area also show the presence of a strong horizontal velocity gradient seismic backstop at a distance of 30 km from the deformation front the seismic wide angle reflections from the top of the subducting oceanic crust constrain the location of the plate boundary offshore dipping at 10 the projection of the epicenter of the maule earthquake onto our derived interplate boundary yielded a hypocenter around 20 km depth this implies that this earthquake nucleated somewhere in the middle of the seismogenic zone neither at its updip nor at its downdip limit

vertical deformation through a complete seismic cycle at isla santa maria chile records of complete earthquake cycles are rare analysis of historical nautical charts and modern gps data that record a full earthquake cycle in chile show that great earthquakes can create small amounts of permanent uplift

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

primitive ultrafine matrix in ordinary chondrites abstract ultrafine matrix material has been concentrated by sieving and filtering disaggregated samples of six ordinary chondrites of different classes this component s holy smoke hs is enriched in both volatile e g na k zn sb and pb as well as refractory elements e g w and ree however the element ratios vary greatly among the different chondrites sem studies show that hs contains fragile crystals differing in composition and apparently in gross disequilibrium not only among themselves but also with the major mineral phases and consequently thermodynamic equilibration did not occur thus hs must have originated from impacting bodies and or was inherent in the primitive regolith subsequent impact brecciation and reheating appears to have altered to varying degrees the original composition of this ultrafine matrix material recent cosmic dust studies may indicate that hs still exists in the solar system survival of such delicate material must be considered in all theories for the origin of chondrites

cumberland falls chondritic inclusions mineralogy petrology of a forsterite chondrite suite abstract as previously found for a chondritic inclusion of unknown affinity mineralogic and petrologic properties of 9 inclusions in the cumberland falls enstatitc achondrite are primitive members of the forsterite f chondrite group hitherto defined by 4 meteorites of similar redox state the inclusions define a primitive suite with properties indicating 8 as f3 and one of even lower petrologic type the abundant minerals include low ca pyroxene olivine plagioclase kamacite taenite schreibersite troilite ferroan alabandite and daubreelite diopside oldhamite and a ti rich sulfide are present in one or two inclusions petrologic textures and jadeitic pyroxene hitherto unidentified in meteorites indicate substantial degree of shock the inclusions acquired their chemical characteristics during nebular condensation and accretion over a broad redox range metal silicate trends in them verify prior s rules their parent body later impacted the enstatite meteorite parent body during impact the inclusions were shocked and incorporated with enstatite achondrite host as a breccia that would become cumberland falls

new kind of type 3 chondrite with a graphite magnetite matrix abstract we have discovered four clasts in three ordinary chondrite regolith breccias which are a new kind of type 3 chondrite like ordinary and carbonaceous type 3 chondrites they have distinct chondrules some of which contain glass highly heterogeneous olivines and pyroxenes and predominantly monoclinic low ca pyroxenes but instead of the usual fine grained fe rich silicate matrix the clasts have a matrix composed largely of aggregates of micron and submicron sized graphite and magnetite the bulk compositions of the clasts as well as the types of chondrules largely porphyritic are typical of type 3 ordinary chondrites although chondrules in the clasts are somewhat smaller 0 1 0 5 mm a close relationship with ordinary chondrites is also indicated by the presence of similar graphite magnetite aggregates in seven type 3 ordinary chondrites this new kind of chondrite is probably the source of the abundant graphite magnetite inclusions in ordinary chondrite regolith breccias and may be more common than indicated by the absence of whole meteorites made of chondrules and graphite magnetite

the solar nebula redox state as recorded by the most reduced chondrules of five primitive chondrites abstract mafic minerals in the most reduced chondrules of five primitive meteorites were analyzed with an electron microprobe to determine the lower limit on their feo contents the accuracy obtained was 0 01 weight percent feo the thermodynamic relationship between mole fraction fesio 3 and po 2 of the ambient nebular gas at the time of mineral equilibration was established and was used to infer the local o h ratio of the nebular gas during chondrule formation the lowest ferrosilite compositions reflected equilibration at 1500k with a gas 2 18 times more oxidizing than a gas of solar composition olivines in low feo uoc chondrules are uniformly more feo rich than coexisting pyroxenes this discrepancy suggests that a significant change in the o h ratio of the nebular gas occurred between the time of olivine and pyroxene crystallization in the region of the nebula where uocs formed mineral compositions in the chondrules of two c2 chondrites studied suggest they formed in a more homogeneous region of the nebula than the uocs

chemical and physical studies of type 3 chondrites i metamorphism related studies of antarctic and other type 3 ordinary chondrites abstract thermoluminescence sensitivity measurements have been made on 18 unequilibrated ordinary chondrites 12 finds from antarctica 5 non antarctic finds and 1 fall the tl sensitivities of these meteorites normalized to dhajala range from 0 034 st mary s county to 2 3 allan hills a78084 and based primarily on these data petrologic type assignments range from 3 3 st mary s county to 3 9 allan hills a78084 although the very low levels of metamorphism experienced by types 3 0 to 3 4 evidently cause large changes in tl sensitivity the new data demonstrate that they are unable to cause any appreciable homogenization of silicate compositions we have therefore slightly revised the silicate heterogeneity ranges corresponding to the lower petrologic types we have discovered that the temperature of maximum tl emission and the broadness of the major tl peak vary systematically with tl sensitivity as tl increases these parameters first decrease and then increase several mechanisms which could account partially or completely for the relationship between tl sensitivity and metamorphism are discussed those which involve the formation of feldspar the tl phosphor in equilibrated meteorites seem to be consistent with the trends in peak temperature and peak width since experiments on terrestrial albite show that the tl peak broadens and moves to higher temperatures as the stable form changes from the low ordered state to the high disordered state the post metamorphism equilibration temperature of type 3 5 meteorites would then correspond to the transformation temperature for the high to low form of meteorite feldspar other factors which may be involved are obscuration of the tl by carbonaceous material changes in the composition of the phosphor and changes in the identity of the phosphor

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

h chondrites trace element clues to their origin we have analyzed 10 h chondrites for 20 trace elements using rnaa the meteorites included 4 of petrologic type 4 and 2 each of types 3 5 and 6 the data show that h chondrites are not isochemical h3 s are depleted by some 10 not only in fe dodd 1976 but also in the siderophiles os re ir ni pd au and ge moreover the abundance pattern of siderophiles varies systematically with petrologic type as similar fractionations of ree have been observed by nakamura 1974 it appears that both the proportions and compositions of the main nebular condensates varied slightly during accretion of the h chondrites thus the higher petrologic types are independent nebular products not metamorphosed descendants of lower petrologic types abundances of highly volatile elements cs br bi tl in cd ar36 correlate with petrologic type declining by 10 3 from type 3 to type 6 the trends differ from those for artificially heated type 3 s ikramuddinet al 1977b herzoget al 1979 but agree passably with theoretical curves for nebular condensation apparently the low volatile contents of higher petrologic types are a primary feature not the result of metamorphic loss the mineralogy of chondrites suggests that they accreted between 405 k absence of fe3o4 and 560 k presence of fes and the abundances of tl bi and in further restrict this interval to 420 500 k accretion at 1070 100 k as proposed by hutchisonet al 1979 1980 leads to some extraordinary problems volatiles must be injected into the parent body after cooling which requires permeation of the body by 1011 times its volume of nebular gas this process must also achieve a uniform distribution of the less volatile elements rb cu ag zn ga ge sn sb se f without freezeout in the colder outer layers factor analysis of our data shows 3 groupings siderophiles os re ir ni pd au and ge volatiles ag br in cd bi and tl and alkalis rb and cs the remaining 5 elements u zn te se and sb remain unassociated

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

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

chemical studies of l chondrites ii shock induced trace element mobilization abstract previous studies of chondrites heated in the laboratory for extended periods under conditions approximating those in shock heated collisional debris indicate that au co se ga rb cs te bi in ag zn tl and cd progress in mobility we report data for these 13 trace elements in 14 l4 6 chondrites of established shock history and discuss these and 13 additional chondrites studied earlier trace element contents vary with petrologic type s fe sub group and shock history the last dominating strongly absolute abundances and interelement relationships for the 6 or 7 most mobile elements vary with degree of shock loading i e residual temperatures established from mineralogic petrologic study a tertiary process shock heating previously known to have affected radiogenic 40 ar and or 4 he in meteorites but not other elements apparently was at least as effective as other open system processes secondary parent body and primary nebular and or accretionary episodes in establishing mobile trace element contents of l chondrites and probably others if conditions during early genetic episodes are to be deduced from compositional information shocked meteorites should be avoided or effects of later processes should be compensated for

chondritic lithic clasts in the cb ch like meteorite isheyevo fragments of previously unsampled parent bodies the cb ch like chondrite isheyevo is characterized by the absence of fine grained interchondrule matrix material the only present fine grained material is found as chondritic lithic clasts in contrast to the pristine high temperature components of isheyevo these clasts experienced extensive aqueous alteration in an asteroidal setting hence the clasts are foreign objects that either accreted together with the high temperature components or were added later to the final isheyevo parent body during regolith gardening in order to constrain the origin and secondary alteration of the clasts in isheyevo we studied their mineralogy petrography structural order of the polyaromatic carbonaceous matter and oxygen isotopic compositions of carbonates three main groups of clasts were defined based on mineralogy and petrology group i clasts consist of phyllosilicates carbonates magnetite and lath shaped fe ni sulfides group ii clasts contain different abundances of anhydrous silicates embedded in a hydrated matrix sulfides magnetite and carbonates are rare with only a few exceptions groups i and ii clasts did not experienced significant thermal metamorphism group iii clasts are characterized by the absence of magnetite and the presence of fe ni metal in addition to aqueous alteration they experienced thermal metamorphism as reflected by the structure of their polyaromatic carbonaceous matter while there are some similarities between the isheyevo clasts ci chondrites and the matrices of cm and cr chondrites on the whole the characteristics of the clasts do not match those of any of these aqueously altered meteorite classes nor do they match those of similar material in various types of chondritic clasts present in other meteorite groups we conclude that the isheyevo clasts represent fragments of previously unsampled parent bodies

the carbon and oxygen isotopic composition of meteoritic carbonates the 13c12c and 18o16o isotopic ratios of carbonates from carbonaceous and ordinary chondrites have been measured on co2 released by the action of h3po4 on whole rock samples carbonates from ci cm and cr carbonaceous chondrites exhibit a range in 18o of ca 15 20 5 to 35 1 relative to smow limited data from co2 water equilibration experiments suggest that meteoritic carbonates do not possess grossly anomalous 17o isotopic compositions therefore they are truly enriched in 13c with 13c between 23 7 and 80 7 relative to pdb large internal variations in 13c and 18o were found in individual meteorites and suggest that two or more isotopically distinct carbonates of different origin may be present the abundance 13c and 18o of carbonate in cm2 chondrites may be related to the extent of aqueous alteration of the meteorites carbonates in ci and cr chondrites have a median 13c ca 50 to 60 whereas 13c of cm meteorites lie in the range 40 to 50 although exceptions exist in both sets of samples cv3 and co3 carbonaceous chondrites and unequilibrated ordinary chondrites release small amounts of co2 on acid treatment which might be from carbonate dissolution but which is not enriched in 13c exhibiting 13c values ca 0 10 the exception to this is bishunpur with 13c ca 23 5 the difference in 13c of the ci cm and cr vs cv co and ordinary chondrite carbonates may be a result of the progressive enrichment in 13c of percolating fluids brought about by increasing solubilization of exotic 13c enriched grains

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

carbon oxygen and nitrogen isotopic compositions of possible martian weathering products in eeta 79001 abstract carbon and oxygen isotopic analyses of carbonate rich white druse material isolated from a contact between lithologies a and c of the eeta 79001 shergottite indicate that this component is probably extraterrestrial in origin and not simply an antarctic weathering product the 13c 6 8 and 18o 21 1 values of the calcium carbonate predominantly calcite are unlike 13 c 18 o combinations of most common terrestrial carbonates whether biogenic or abiogenic however 13c and 18o of the carbonates in eeta 79001 are very similar to the corresponding values for carbonates analysed from nakhla a meteorite closely allied to shergottites it seems apparent that the carbonate minerals in these snc meteorites were formed on the meteorites parent body mars isotopic analysis of nitrogen liberated during combustion of a carbonate rich fraction of eeta 79001 does not give any clear evidence for the 15n enriched component isolated from eeta 79001 lithology c glass and postulated as trapped martian atmosphere however substantial amounts of nitrogen were present the origin of these components is unclear but the low temperature of release poses some constraints

experimental studies of condensation processes of silicate materials at low pressures and high temperatures i phase equilibria in the system camgsi2o6h2 in the temperature range 1200 1500 c and the pressure range ph2 10 6 to 10 9 bar phase equilibria in the system camgsi2o6h2 in the pressure and temperature ranges 10 9 to 10 6 bar and 1200 1500 c respectively have been experimentally determined the vaporous curve was determined by monitoring evaporation rate and compositional changes as a function of temperature crystalline diopside condenses from a gas phase along a vaporous curve with a positive slope of approximately 16 c log unitph2 bars from about 1360 c atph2 10 9 bar to 1388 c at 3 10 7 bar partially evaporated diopside at temperatures above its vaporous shows but systematic increase in ca mg with time and degree of evaporation there were no chemical changes with time and degree of evaporation of diopside within its own stability field at higher pressures a liquid condenses from the vapor with a slope of the liquid vapor curve of about 50 c log unitph2 bars the liquidus temperature decreases from 1388 c near the triple point to about 1350 c atph2 10 6 bar and is nearly vertical toph2 1 bar the ca mg of the liquid exceeds 1 indicating incongruent melting behavior although no additional crystalline phases were observed liquid diopside probably also evaporates incongruently provided that the phase equilibria of the diopside composition mimic those of other refractory phases condensing from the early solar nebula and that only h2 gas was present the experimental results indicate that the pressures in the nebula during condensation of crystals from vapor were significantly lower 10 4 bar alternatively if the higher pressure estimates are correct liquid silicate will condense from the vapor and vapor liquid and crystal liquid equilibria were more important during the petrogenetic processes resulting in aggregated silicate materials than suggested previously

matrix and fine grained rims in the unequilibrated co3 chondrite alha77307 origins and evidence for diverse primitive nebular dust components abstract the mineralogical and chemical characteristics of dark matrix and fine grained rims in the unequilibrated co3 chondrite alha77307 have been investigated in detail by scanning electron microscopy electron microprobe analysis and transmission electron microscopy matrix and fine grained rims on chondrules and other objects are compositionally homogeneous on the scale of 10 m and there are no compositional differences between matrix and rims mineralogically both the matrix and rims are extremely diverse and consist of a highly unequilibrated assemblage of si and fe rich amorphous material olivine pyroxene fe ni metal magnetite pentlandite pyrrhotite anhydrite and mixed layer phyllosilicate phases several distinct components can be recognized within the matrix and rims based on their textural and compositional characteristics which appear to represent basic fine grained units of nebular dust the microstructures of these different components show that they have experienced significantly different thermal histories unlike the ordinary chondrites an origin for any significant component of the matrix or rims in alha77307 from chondrules is improbable based on compositional and microstructural evidence the matrix and rim components in alha77307 formed by disequilibrium condensation processes as fine grained amorphous dust that is represented by the abundant amorphous component in the matrix such condensation could have occurred under a variety of conditions at different times and locations within the solar nebula or possibly earlier in a circumstellar environment subsequent thermal processing of this primitive condensate material in a variety of environments in the nebula resulted in partial or complete recrystallization of the fine grained dust the intimate association of fine grained components with disparate compositions and thermal histories shows that mixing of fine grained dust within the nebula must have been extremely thorough

graphite magnetite aggregates in ordinary chondritic meteorites aggregates consisting largely of submicrometre graphite and magnetite crystals have been identified in 14 unequilibrated and regolith breccia ordinary chondrites like other primitive components they formed before the meteorites accreted chondrite clasts rich in graphite magnetite occur in three regolith breccias and are a new kind of unequilibrated ordinary chondrite they were probably the source of graphite magnetite aggregates in regolith breccias

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

discovery of hg cu bearing metal sulfide assemblages in a primitive h 3 chondrite towards a new insight in early solar system processes we report here the discovery of a novel meteoritic paragenesis consisting of sub micrometric hgs cu sulfides and hg metal associated with polycrystalline fine grained native cu in opaque mineral aggregates heterogeneously distributed in the matrix of the h 3 tieschitz unequilibrated ordinary chondrite uoc the systematic association of hg with cu in tieschitz chondrite provides a unique opportunity to place robust constraints on the origin of these assemblages either by condensation and sulfidation in a local nebular reservoir of non solar composition followed by gentle and fast accretion or by sublimation of hg from the hot interior of the asteroid and recondensation in its cold outer regions the sulfide phase relations support low temperature conditions 300 c implying that subsequent to accretion indigenous hydrothermal processing oxidation sulfidation transportation or shock induced thermal processing of the assemblage on the parent body earlier proposed are very unlikely and unrealistic origin of hgs by sublimation of hg from the hotter asteroid interior and precipitation as cinnabar in the colder surface regions is discrepant with our findings and can be ruled out because cinnabar occurs only in tieschitz matrix in alternating rhythmic intergrowth with cu sulfide the sublimation scenario calls for co evaporation of both the highly volatile hg as hgs and hg metal and the moderately volatile cu both as cu metal or their sulfides and deposition as sulfides in alternating episodes our findings provide further ample evidence refuting the repeated claim of formation of native copper in chondritic metal by shock induced impact melting cold accretion is the only reasonable possibility to preserve the delicate accretionary intergrowth textures the polycrystallinity of feni metal native cu hg cu sulfides and native hg globules and the high hg concentration retained in this meteorite our findings strongly suggest that tieschitz resided near the cold surface of the parent asteroid

cumberland falls chondritic inclusions ii trace element contents of forsterite chondrites and meteorites of similar redox state abstract mineralogic study of black inclusions in the cumberland falls enstatite achondrite revealed that they constitute a highly unequilibrated chondritic suite distinct from other chondrite groups this highly shocked suite the forsterite f chondrites exhibits mineralogic trends apparently produced during primary nebular condensation and accretion over a broad redox range we analyzed these samples and possibly related meteorites for ag as au bi cd co cs ga in rb sb se te tl u and zn trace elements known to yield important genetic information the results demonstrate the compositional coherence and distinctiveness of the f chondrite suite relative to other chondrites the antarctic aubrite alh a78113 may include more f chondrite material trace element contents do not vary with mineral compositions hence do not reflect redox variations during formation of f chondrite parental matter trace element mobilization during secondary heating episodes in the f chondrite parent or during its disruptive collision with the enstatite meteorite parent body is not detectable chemical trends in f chondrites apparently reflect primary nebular processes cosmochemical fractionation of lithophiles from siderophiles and chalcophiles occurred at moderately high temperatures certainly higher than those existing during formation of primitive carbonaceous enstatite and ordinary chondrites of petrologic type 3

impact melting in the cumberland falls and mayo belwa aubrites abstract six chondritic clasts in the cumberland falls polymict breccia were examined four texturally resemble ordinary chondrites ocs and two are impact melt breccias containing shocked oc clasts adjacent to a melt matrix the six chondritic clasts are probably remnants of a single oc projectile that was heterogeneously shocked when it collided with the cumberland falls host mayo belwa is the first known aubrite impact melt breccia it contains coarse enstatite grains exhibiting mosaic extinction the enstatite grains are surrounded by a melt matrix composed of 3 16 m size euhedral and subhedral enstatite grains embedded in sodic plagioclase numerous vugs ranging from a few micrometers to a few millimeters in size constitute 5 vol of the meteorite they occur nearly exclusively within the mayo belwa matrix literature data show that some vugs are lined with bundles of acicular grains of the amphibole fluor richterite this phase has been reported previously in only two other enstatite meteorites abee and st sauveur both of which are eh chondrite impact melt breccias it seems likely that in mayo belwa volatiles were vaporized during an impact event and formed bubbles in the melt as the melt solidified the bubbles became cavities plagioclase and fluor richterite crystallized at the margins of these cavities via reaction of the melt with the vapor

indicators of parent body processes hydrated chondrules and fine grained rims in the mokoia cv3 carbonaceous chondrite abstract a petrographic and electron microscopic study of the mokoia cv3 carbonaceous chondrite shows that all of the chondrules and inclusions 400 m in diameter and most of their fine grained rims studied referred to as chondrules rims contain various amounts of hydrous phyllosilicates mostly saponite formed by aqueous alteration of anhydrous silicates the rims mainly consist of fine grained olivine and saponite in varying proportions and contain crosscutting veins of fe rich olivine the boundaries between the chondrules and their rims are irregular and show abundant evidence of aqueous alteration interactions between them in contrast the host matrix contains very minor amounts of saponite and shows no evidence of such extensive aqueous alteration the boundaries between the chondrules rims and the matrix are sharp and show no traces of the matrix having been involved in the alteration of the chondrules rims these observations indicate that the aqueous alteration in the chondrules rims did not occur in the present setting we suggest that the chondrules rims are actually clasts transported from a location on the meteorite parent body different from where the mokoia meteorite was from the aqueous alteration of the chondrules rims probably occurred there the veins in the rims were originally fractures produced in an interchondrule matrix by impacts these were later filled by fe rich olivine during aqueous activity this location was then involved in impact brecciation and individual chondrules were ejected as clasts with remnants of the matrix surrounding them during the continuing brecciation those chondrule rim clasts were transported mixed with anhydrous matrix grains and finally lithified to the present meteorite therefore the rims are fragmented remnants of a former matrix textures characterized by fine grained rims surrounding chondrules in chondrites have been widely thought to have formed in the solar nebula before they accreted into their parent bodies however our results suggest that some textures may not be explained by such an accretionary model instead the multi stage parent body process modeled for the mokoia rim formation may be a more plausible explanation

the ungrouped chondrite el medano 301 and its comparison with other reduced ordinary chondrites abstract el medano 301 em 301 is an ungrouped chondrite with overall texture and trace element distribution similar to those of ordinary chondrites ocs but with silicate olivine and low ca pyroxene compositions that are more reduced than those in ocs with average olivine and low ca pyroxene of fa3 9 0 3 and fs12 8 4 9 respectively these values are far lower than the values for ocs and even for chondrites designed as reduced chondrites low ca pyroxene is the dominant mineral phase and shows zoning with higher mgo contents along the crystal rims and cracks reverse zoning the co content of kamacite is also much lower than the concentrations observed in ocs below detection limit of 0 18 wt versus 0 44 37 wt oxygen isotopic composition is 17o 0 79 0 78 and slightly different from that of ocs the lower modal olivine pyroxene ratio different infrared ir spectra lower co content of kamacite lower mean feo contents of olivine and pyroxene different kamacite texture and different oxygen isotopic composition show that em 301 does not belong to a known oc group em 301 shows similarities with chondritic clasts in cumberland falls aubrite and with northwest africa 7135 nwa 7135 and acfer 370 ungrouped chondrites however dissimilar to nwa 7135 and the clasts it does not contain highly reduced mineral phases like daubreelite our observations suggest the formation of em 301 in a nebular region compositionally similar to ocs but with a different redox state with oxygen fugacity o2 in this region lower than that of ocs and higher than that of enstatite chondrites condensation region a second possibly nebular phase of reduction by the production of reducing gas phases e g c rich could be responsible for the subsequent reduction of the primary material and the occurrence of reverse zoning in the low ca pyroxene and lower average fa fs ratio based on the ir spectra of em 301 we suggest the possibility that the parent body of this chondrite was a v type asteroid

the galim ll eh polymict breccia evidence for impact induced exchange between reduced and oxidized meteoritic material galim is a polymict breccia consisting of a heavily shocked shock stage s6 ll6 chondrite galim a and an impact melted eh chondrite galim b relict chondrules in galim b served as nucleation sites for euhedral enstatite grains crystallizing from the impact melt many of the reduced phases typical of eh chondrites e g si bearing metallic fe ni ti bearing troilite are absent galim b was probably shock melted while in contact with a more oxidized source namely galim a during this event si was oxidized from the metal and ti was oxidized from troilite galim a contains shock veins and recrystallized unzoned olivine the absence of evidence for reduction in galim a may indicate that the amount of ll material greatly exceeded that of eh material shock metamorphism may have taken place on the ll parent body shock induced redox reactions such as those inferred for the galim breccia appear to be restricted mainly to asteroids because the low end tail of their relative velocity distribution permits mixing of intact disparate materials including accretion of projectiles of different oxidation states whereas the peak of the distribution leads to high equilibration shock pressures allowing impact induced exchange between previously accreted disequilibrated materials galim probably formed by a two stage process 1 accretion to the ll parent body of an intact eh projectile at low relative velocities and 2 shock metamorphism of the assemblage by the subsequent impact of another projectile at significantly higher relative velocities

the onset of metamorphism in ordinary and carbonaceous chondrites ordinary and carbonaceous chondrites of the lowest petrologic types were surveyed by xray mapping techniques a variety of metamorphic effects were noted and subjected to detailed analysis using electron microprobe scanning electron microscopy sem transmission electron microscopy tem and cathodoluminescence cl methods the distribution of cr in feo rich olivine systematically changes as metamorphism increases between type 3 0 and type 3 2 igneous zoning patterns are replaced by complex ones and cr rich coatings develop on all grains cr distributions in olivine are controlled by the exsolution of a cr rich phase probably chromite cr in olivine may have been partly present as tetrahedrally coordinated cr3 separation of chromite is nearly complete by petrologic type 3 2 the abundance of chondrules showing an inhomogeneous distribution of alkalis in mesostasis also increases with petrologic type tem shows this to be the result of crystallization of albite residual glass compositions systematically change during metamorphism becoming increasingly rich in k glass in type i chondrules also gains alkalis during metamorphism both types of chondrules were open to an exchange of alkalis with opaque matrix and other chondrules the matrix in the least metamorphosed chondrites is rich in s and na the s is lost from the matrix at the earliest stages of metamorphism due to coalescence of minute grains progressive heating also results in the loss of sulfides from chondrule rims and increases sulfide abundances in coarse matrix assemblages as well as inside chondrules alkalis initially leave the matrix and enter chondrules during early metamorphism feldspar subsequently nucleates in the matrix and na re enters from chondrules these metamorphic trends can be used to refine classification schemes for chondrites cr distributions in olivine are a highly effective tool for assigning petrologic types to the most primitive meteorites and can be used to subdivide types 3 0 and 3 1 into types 3 00 through 3 15 on this basis the most primitive ordinary chondrite known is semarkona although even this meteorite has experienced a small amount of metamorphism allan hills alh a77307 is the least metamorphosed co chondrite and shares many properties with the ungrouped carbonaceous chondrite acfer 094 analytical problems are significant for glasses in type ii chondrules as na is easily lost during microprobe analysis as a result existing schemes for chondrule classification that are based on the alkali content of glasses need to be revised

chemical and physical studies of type 3 chondrites vi siderophile elements in ordinary chondrites abstract the abundances of fe ni co au ir ga as and mg have been determined by instrumental neutron activation analysis in 38 type 3 ordinary chondrites 10 of which may be paired and 15 equilibrated chondrites classification of type 3 ordinary chondrites into the h l and ll classes using oxygen isotopes and parameters which reflect oxidation state fa and fs in the olivine and pyroxene and co in kamacite is difficult or impossible bulk compositional parameters based on the equilibrated chondrites have therefore been used to classify the type 3 chondrites the distribution of the type 3 ordinary chondrites over the classes is very different from that of the equilibrated chondrites the ll chondrites being more heavily represented the type 3 ordinary chondrites contain 5 to 15 percent lower abundances of siderophile elements and a compilation of the present data and literature data indicates a small systematic decrease in siderophile element concentration with decreasing petrologic type the type 3 ordinary chondrites have like the equilibrated ordinary chondrites suffered a fractionation of their siderophile elements but the loss of ni in comparison with au and ir is greater for the type 3 chondrites these siderophile element trends were established at the nebula phase of chondritic history and the co variation with petrologic type implies onion shell structures for the ordinary chondrite parent bodies it is also clear that the relationship between the type 3 and the equilibrated ordinary chondrites involves more than simple closed system metamorphism

chemical isotopic and mineralogical evidence for the origin of matrix in ordinary chondrites abstract we report the first combined chemical isotopic and mineralogical study of fine grained opaque matrix material from a type 3 ordinary chondrite allan hills a77299 h3 7 electron microprobe and instrumental neutron activation analysis of a large matrix lump show that it has a major element composition typical of matrix material in type 3 chondrites unlike chondrules it shows no siderophile element depletions and is remarkably unfractionated relative to ci chondrites suggesting that it is primitive solar system material the matrix lump has an unique oxygen isotopic composition which lies below the terrestrial fractionation line and differs markedly from the composition of fine grained matrix lumps and chondrule rims from semarkona grossman et al 1987 transmission electron microscope tem studies of microtomed samples of the fine grained fraction m of the matrix lump show that it consists of rare angular clastic grains 1 m of pyroxene and olivine embedded within a groundmass of rounded fine grained m olivines the mineralogy and textures of the matrix lump are typical of other occurrences of fine grained matrix studied by tem in other type 3 ordinary chondrites we conclude that the matrix lump in alha 77299 consists largely of material that formed by annealing of amorphous presolar dust or nebular condensates and could not have been derived from chondrules by any reasonable mechanism however the observed compositional differences between the matrix lump and chondrules in ordinary chondrites are consistent with the idea that some chondrules formed by melting of matrix like material accompanied by loss of siderophile and volatile elements

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

microchondrules in ordinary chondrites implications for chondrule formation abstract previous studies of ordinary chondrites oc reported isolated microchondrules within the fine grained or clastic matrix of many type 3 samples larger sets of microchondrules have also been found as rare clasts in type 3 oc we report here another major setting for microchondrules large numbers n 100 of microchondrules 40 m in apparent diameter occur together with irregularly shaped fragments in fine grained rims around four low feo porphyritic olivine chondrules and one barred olivine chondrule these chondrules are from ll3 1 bishunpur l3 4 eet90161 l3 4 eet90261 ll3 4 piancaldoli and ll3 0 semarkona the two kinds of microchondrules observed are 1 numerous low feo radial and cryptocrystalline microchondrules consisting of low ca pyroxene and 2 relatively rare high feo olivine microchondrules both types of microchondrules are embedded in high feo fine grained matrix materials they are typically accompanied by irregularly shaped pyroxene fragments that form a continuum in composition and shape with the low feo microchondrules the pyroxene rich surfaces of the host chondrules project into the surrounding rims as peninsulas with rounded embayments consistent with remelting although on average less ferroan the peninsulas overlap the fragments and low feo microchondrules in composition and appear to have been the main source of these objects the occurrence of numerous low feo pyroxene rich microchondrules with similar textures and compositions within high feo fine grained matrix rims around normal size chondrules and the apparent remelting of the surfaces of the host chondrules indicate that the microchondrules formed after solidification of the host chondrules mainly by remelting of their pyroxene rich surfaces or possibly igneous rims the remnants of these pyroxene rich rims are preserved as peninsulas extending outward from the chondrule surface and as irregularly shaped pyroxene fragments coexisting with the microchondrules because a newly formed microchondrule cloud in the nebula would dissipate quickly due to random motions of the individual microchondrules it seems inescapable that the fine grained material which now surrounds the microchondrules was in their immediate vicinity when they formed and served as a trapping matrix the material probably occurred as a highly porous aerogel like aggregate of feo rich nebular dust the rare high feo olivine microchondrules probably formed at the same time as the low feo pyroxene microchondrules by melting adjacent portions of the porous dust

carbon isotope relationships in winonaites and forsterite chondrites abstract the unusual stone meteorites winona mt morris wisconsin pontlyfni kakangari and acapulco plus a chondritic inclusion from the cumberland falls aubrite have been analyzed for their carbon content and isotopic composition in order to determine whether similarities exist between all or some of the meteorites the technique employed for these determinations was one of combustion in steps from room temperature to 1200 c allowing distinction between different carbon containing species present winona mt morris wis pontlyfni and the chondritic inclusion from cumberland falls all behave in a common fashion during combustion the major indigenous carbon component in these specimens is graphite with a 13 c value of between 9 5 and 2 8 close to the range reported for graphite in both enstatite chondrites and iab irons thus the links proposed to exist between winonaites silicates from iabs and e chondrites from oxygen isotopes and major element chemistry are also apparent for carbon kakangari is clearly different from winonaites and there is no basis for including this meteorite in any group with iab irons or enstatite chondrites silicates from acapulco may have some links with winonaites but the carbon isotopic composition of graphite precipitated from metal 13 c 20 and from the element still in solid solution 13 c 28 suggest that the iron nickel portions of the meteorites are unrelated

post earthquake coastal evolution and recovery of an embayed beach in central southern chile abstract earthquakes and tsunamis are significant factors for change along active margin shores and influence coastal evolution the chilean coast was affected in 2010 by a subduction earthquake with a magnitude of mw 8 8 and also by a trans pacific tsunami which generated violent geomorphologic changes and damaged homes following these events the magnitude of the changes which affect chile s central southern coast 37 s and the role of subduction earthquakes in coastal evolution on a historical scale were investigated at lebu bay an embayed beach data were generated for variations in time and space along the shoreline topographical and bathymetric changes in the bay and for morphodynamic littoral processes logarithmic and parabolic models were applied to the shoreline along with map overlays in order to determine changes the shoreline processes were analyzed based on statistics for waves tides and sediment transport for pre and post tsunami conditions an average accretion rate of 2 80 m year 1984 2010 was established for the shoreline with a strong trend towards accretion in the last 30 years a parabolic function best represented the general form of the shoreline although the presence of a river in the concave zone affected the fit in this sector two factors controlled historical changes on the beach one of anthropic origin in addition to the earthquake and tsunami on february 27th 2010 the post earthquake recovery was fast and currently the beach is in a stable condition despite the inter seismic subsidence process previous to the event this coastal system showed a high resilience in the face of coastal geomorphological changes induced by high impact natural disturbances however the opposite occurred in relation to changes induced by anthropogenic disturbances

siderophile trace elements in metals and sulfides in enstatite achondrites record planetary differentiation in an enstatite chondritic parent body abstract siderophile element concentrations were measured by la icp ms in metals and sulfides from five aubrite meteorites siderophile element patterns in aubrites are either similar to those in metal from enstatite chondrites or can be derived by crystallization from metallic liquids derived by partial melting of e chondrites some metal grains in mt egerton cumberland falls and aubres show moderate to severe depletion in compatible highly siderophile elements re os ir ru which are consistent with solid metal liquid metal differentiation of enstatite chondrite like metal metals from chondrite inclusions in cumberland falls show more extremely fractionated patterns than those from the aubritic matrix potentially hinting at fractionation and partial melting processes affecting not only the aubrite parent body but the chondrite body from which the inclusions were derived as well models using experimental partition coefficients show that aubrite metal chemically corresponds to solid metal segregated during differentiation of primary metallic liquids of eh el composition that contained both substantial s and c contents this result is consistent with a genetic link between enstatite chondrites and aubrites but as to whether aubrites were derived from the same body ies as enstatite chondrites or have their origin in multiple and potentially separated bodies cannot be answered unequivocally with chemical or isotopic data alone

metamorphic temperatures in the michigamme formation compared with the thermal effect of an intrusion northern michigan temperature and pressure conditions of metamorphism in the peavy node area in northern michigan have been estimated from the garnet biotite geothermometer and garnet plagioclase aluminosilicate quartz geobarometer sillimanite zone rocks yielded an average temperature 592 c in the staurolite zone temperatures ranged from 545 to 582 c and in the garnet zone temperature estimates were 485 to 557 c the pressure estimate of sillimanite bearing assemblages is 4 4 kb whilst that of andalusite bearing rocks is 2 9 kb at 534 c temperatures due to the peavy pond complex pvc intrusion as a heat source were calculated at various positions within the michigamme fm assuming that the magma was emplaced at 1000 c and taking into account the latent heat of solidification of magma and the heat consumed by metamorphic dehydration reactions if cooling proceeds by conduction a one dimensional 3 2 km thick sheet heat source reaches a maximum temperature of 355 c at 2 5 km from contact within the staurolite zone dur

fayalitic olivine in matrix of the krymka ll3 1 chondrite vapor solid growth in the solar nebula fayalitic olivine fa54 94 is a ubiquitous component in the matrix of krymka ll3 1 as well as in other highly unequilibrated chondrites ordinary and carbonaceous in krymka the fayalitic olivine has an unusual anisotropic platy morphology that occurs in at least five types of textural settings that can be characterized as 1 isolated platelets 2 clusters of platelets 3 euhedral to subhedral crystals 4 overgrowths of platelets on forsteritic olivine and 5 fluffy porous aggregates from transmission electron microscope tem investigation the direction of elongation of the platy olivine overgrowths on forsteritic olivine substrates is along the c axis and in most cases it corresponds with the c axis of the substrate olivine which suggests that the fayalitic olivine grew in this unusual morphology and is not a replacement product of preexisting material the fayalitic olivine in the matrix of krymka is compositionally similar to olivine with platy morphology in the matrix of some cv3 chondrites and both have similar fe mn ratios but important morphological differences indicate that their relationship needs to be explored further textural and compositional data indicate that the fayalitic olivine in the matrix of krymka as well as in some other unequilibrated ordinary chondrites formed prior to final lithification of the meteorite and probably prior to parent body accretion we find that formation of the fayalitic olivine by vapor solid growth provides the best explanation for our observations and data and is the only feasible mechanism for the formation of fayalitic olivine in the matrix of krymka we propose that the fayalitic olivine formed by vaporization and recondensation of olivine rich dust during a period of enhanced dust gas ratio in the nebula

the evolution of partially differentiated planetesimals evidence from iron meteorite groups iab and iiicd group iab irons probably come from a parent body that partially differentiated into a sulfur rich molten core and a primitive silicate outer layer in which only minor or localized melting occurred although the complexity of meteorites from this parent body or bodies irons with and without massive silicate inclusions stony meteorites like winona sulfide rich meteorites like mundrabilla etc implies a complicated history the partial differentiation model is consistent with most properties of these meteorites the behavior of five model parent bodies of different composition during heating to 1400 k the temperature recorded in many i ab silicates shows that meteorites like iab irons can form by this process sulfide rich parent bodies differentiate into a liquid s rich core and a primitive metal bearing mantle around 1230 k but in parent bodies lower in sulfide abundance this process may be delayed until minor melting of silicates occurs 1370 30 k in most cases any silicate melt that may have formed resolidified in situ the sulfide melt fractionally crystallized along the fe ni fes cotectic some melt was injected into silicates to form copiapo type breccias considerations of graphite metal silicate equilibrium and the retention of noble gases suggest that brecciated iabs formed at depth inside a moderately large a few tens to a hundred kilometers parent body the correlation of i xe ages with ni content is interpreted as the result of an excess 129xe component associated with the s rich melt which increases with melt evolution

igneous rims on low feo and high feo chondrules in ordinary chondrites abstract many ordinary chondrite oc chondrules are surrounded by rims that show evidence of appreciable melting and can be called igneous these rims formed after the melting and solidification of the host chondrule we studied thirteen igneous rims on low feo chondrules fa or fs 10 mol in ordinary chondrites of petrographic type 3 5 by electron microprobe analysis and scanning electron microscopy in both sets olivine and pyroxene compositions of the rims are similar to or moderately higher in feo than those in the host igneous rims around low feo chondrules show evidence of large degree 80 melting including 1 resorbed chondrule surfaces 2 rounded metal troilite nodules and feldspathic mesostasis 3 euhedral and subhedral morphology of olivine and pyroxene and limited ranges in grain sizes and 4 a rarity of relict grains most low feo chondrules have olivine as their major phase but pyroxene is commonly the predominant phase in their rims rims on high feo chondrules generally have smaller grain sizes and exhibit lower degrees of melting than rims around low feo chondrules mg rich relict grains are observed in high feo rims most low feo chondrules have matrix like rims around the igneous rims but matrix like rims are rare around rims on high feo chondrules there is a continuum between igneous rims and enveloping secondaries of compound chondrules the existence of both sets of objects supports the view that in the oc region most mm size grain assemblages experienced more than one melting event the precursors melted to produce the igneous rims on low feo chondrules differ from those that comprise the rims on high feo chondrules a sizeable fraction of the precursors of low feo rims are from the host chondrule most high feo rims appear to consist largely of melted matrix like materials if the rim precursors are mainly independent the similar fa and fs contents in mafic minerals of rims and host chondrules indicate that 1 oc nebular subregions bounded in space and or in time were dominated by well mixed solids 2 many chondrules experienced multiple heating events during a short period and were then withdrawn from the chondrule forming region and 3 chondrules formed at different times were mixed before agglomeration to form chondrites if the host chondrules were the main source of the low feo rim materials the fact that pyroxene is generally more abundant than in the host suggests that sio 2 normative matrix was also an important ingredient and or that kinetics favored pyroxene crystallization in the rim rims around high feo chondrules were heated to lower temperatures than rims around low feo chondrules the rarity of matrix like rims around high feo igneous rims may indicate that the dust chondrule ratio was lower where they formed

segmentation of megathrust rupture zones from fore arc deformation patterns over hundreds to millions of years arauco peninsula chile 1 this work explores the control of fore arc structure on segmentation of megathrust earthquake ruptures using coastal geomorphic markers the arauco nahuelbuta region at the south central chile margin constitutes an anomalous fore arc sector in terms of topography geology and exhumation located within the overlap between the concepcion and valdivia megathrust segments this boundary however is only based on 500 years of historical records we integrate deformed marine terraces dated by cosmogenic nuclides syntectonic sediments published fission track data seismic reflection profiles and microseismicity to analyze this earthquake boundary over 10 2 10 6 years rapid exhumation of nahuelbuta s dome like core started at 4 1 2 ma coeval with inversion of the adjacent arauco basin resulting in emergence of the arauco peninsula here similarities between topography spatiotemporal trends in fission track ages pliocene pleistocene growth strata and folded marine terraces suggest that margin parallel shortening has dominated since pliocene time this shortening likely results from translation of a fore arc sliver or microplate decoupled from south america by an intra arc strike slip fault microplate collision against a buttress leads to localized uplift at arauco accrued by deep seated reverse faults as well as incipient oroclinal bending the extent of the valdivia segment which ruptured last in 1960 with an mw 9 5 event equals the inferred microplate we propose that mechanical homogeneity of the fore arc microplate delimits the valdivia segment and that a marked discontinuity in the continental basement at arauco acts as an inhomogeneous barrier controlling nucleation and propagation of 1960 type ruptures as microplate related deformation occurs since the pliocene we propose that this earthquake boundary and the extent of the valdivia segment are spatially stable seismotectonic features at million year scale

the origin of aubrites evidence from lithophile trace element abundances and oxygen isotope compositions abstract we report the abundances of a selected set of lithophile trace elements including lanthanides actinides and high field strength elements and high precision oxygen isotope analyses of a comprehensive suite of aubrites two distinct groups of aubrites can be distinguished a the main group aubrites display flat or light ree depleted ree patterns with variable eu and y anomalies their pyroxenes are light ree depleted and show marked negative eu anomalies b the mount egerton enstatites and the silicate fraction from larned display distinctive light ree enrichments and high th sm ratios mount egerton pyroxenes have much less pronounced negative eu anomalies than pyroxenes from the main group aubrites leaching experiments were undertaken to investigate the contribution of sulfides to the whole rock budget of the main group aubrites sulfides contain in most cases at least 50 of the rees and of the actinides among the elements we have analyzed those displaying the strongest lithophile behaviors are rb ba sr and sc the homogeneity of the 17 o values obtained for main group aubrite falls 17 o 0 009 0 010 2 suggests that they originated from a single parent body whose differentiation involved an early phase of large scale melting that may have led to the development of a magma ocean this interpretation is at first glance in agreement with the limited variability of the shapes of the ree patterns of these aubrites however the trace element concentrations of their phases cannot be used to discuss this hypothesis because their igneous trace element signatures have been modified by subsolidus exchange finally despite similar o isotopic compositions the marked light ree enrichments displayed by mount egerton and larned suggest that they are unrelated to the main group aubrites and probably originated from a distinct parent body

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

reflectance spectra of featureless materials and the surface mineralogies of m and e class asteroids this study was supported by grants in aid of research from the central research fund of the university of alberta to d g w s from sigma xi the scientific research society and the geological society of america 3741 87 to e a c and nasa planetary geology and geophysics grant nagw 642 to m j g

chemical and physical studies of chondrites x cathodoluminescence and phase composition studies of metamorphism and nebular processes in chondrules of type 3 ordinary chondrites abstract the cathodoluminescence cl properties of eight type 3 ordinary chondrites and one l5 chondrite have been determined and phenocryst and mesostasis compositions have been analyzed in the chondrules of four of them semarkona type 3 0 krymka 3 1 allan hills a77214 3 5 and dhajala 3 8 in order to investigate their origins and metamorphic history two major classes of chondrule with eight subdivisions have been identified mainly on the basis of cl properties and 95 of the chondrules can be assigned to these groups on the basis of phenocryst and mesostasis composition class a chondrules consisting of those with plagioclase normative mesostasis with bright cl are subdivided into groups a1 a2 a3 a4 and a5 class b chondrules with little or no cl and having quartz normative mesostases in the least metamorphosed chondrites which becomes feldspathic with metamorphism are subdivided into groups b1 b2 and b3 relationships between the eight chondrule groups can be deduced from their relative abundance in each of the nine chondrites groups a1 a2 b1 and a5 are present in semarkona 15 20 60 5 by number respectively group a5 chondrules in semarkona being more heterogeneous than a5 chondrules in chondrites of higher petrologic type chondrule group a1 evolves into a3 then a4 and then a5 during metamorphism while a2 evolves into a4 and then a5 chondrule group b1 evolves into b2 b3 and then a5 but higher levels of metamorphism are required to complete the series than for the a1 5 series conversion of a group to an adjacent group can be observed in allan hills a77214 3 5 where several chondrules are group b3 in their central regions and group a5 in their outer regions the present chondrule groups are essentially independent of texture since group a and group b chondrules differ in bulk composition redox state and possibly oxygen isotope systematics their relative abundance might be a factor in the creation of the nine chondrite classes

land level changes produced by the mw 8 8 2010 chilean earthquake we observed vertically displaced coastal and river markers after the 27 february 2010 chilean earthquake moment magnitude mw 8 8 land level changes range between 2 5 and 1 meters evident along an approximately 500 kilometers long segment identified here as the maximum length of coseismic rupture a hinge line located 120 kilometers from the trench separates uplifted areas to the west from subsided regions a simple elastic dislocation model fits these observations well model parameters give a similar seismic moment to seismological estimates and suggest that most of the plate convergence since the 1835 great earthquake was elastically stored and then released during this event

the cosmochemical behavior of mercury abstract we review long standing reports of both the hg paradox that hg abundances in meteorites are inconsistent with its volatile behavior and the anomalous 196 hg 202 hg ratios in all types of extraterrestrial material a careful study of the literature suggests that both results may be due to overestimation of 202 hg abundances from neutron activation analysis we reevaluate hg condensation in the solar nebula using both volatility trends for chondritic meteorites and thermodynamic calculations the extent of hg depletion in allende indicates a 50 condensation temperature of 350 k thermodynamic calculations show that hg condenses into various metal alloys at 300 k or lower at lower temperatures hg can be incorporated into fe ni sulfides as a trace element we investigate chemisorption as a method for incorporating hg into solid material in the solar nebula a large fraction of hg can chemisorb on metal surfaces at temperatures as high as 515 k depending on the grain size

deciphering the nebular and asteroidal record of silicates and organic material in the matrix of the reduced cv3 chondrite vigarano we have conducted scanning electron microscope sem and transmission electron microscope tem studies of a variety of occurrences of matrix in the reduced cv3 chondrite breccia vigarano matrix which occurs as clastic interchondrule material and finer grained rims is dominated by morphologically variable olivines that host submicron hercynitic spinel and carbonaceous inclusions clastic matrix and fine grained rims show significant differences in their olivine morphologies abundance and composition of olivine inclusions and characteristics of the carbonaceous matter we suggest that these differences are the result of different degrees of alteration of clastic matrix and rims and are not due to variability in their precursor materials textural and compositional characteristics of olivine in the matrix are consistent with formation by growth possibly from an amorphous precursor material during asteroidal metamorphism in the presence of limited quantities of aqueous fluids spinel inclusions in olivine may be nebular condensates that acted as seeds for nucleation of olivine or may have formed during metamorphism and were subsequently overgrown by olivine carbonaceous material occurs as nanometer sized inclusions within olivine in both fine grained rims and clastic matrix but is most abundant as 100 200 nm grains interstitial to matrix olivines most carbonaceous material is amorphous but poorly graphitized carbon pgc also occurs as a minor component in both olivine inclusions and interstitial c the widespread occurrence of fine grained amorphous carbon grains in the interstitial regions between olivine grains may preserve the distribution and grain size of nebular organic material no clear textural relationships exist between carbonaceous grains and the other mineralogical components of vigarano matrix that could help constrain the origin of the organic grains i e evidence for fischer tropsch type reactions finally there are considerable differences between matrix olivines in vigarano in comparison with those in oxidized cv3 chondrites in particular the mineralogy and morphology of the matrix olivines and the nature composition and distribution of inclusions in the olivine grains are distinct based on these differences we conclude that matrix in the oxidized cv3 chondrites could not have formed by thermal processing of vigarano like material

coastal uplift and mortality of intertidal organisms caused by the september 1985 mexico earthquakes coastal uplift associated with the great mexican earthquake of 19 september 1985 and its principal aftershock produced widespread mortality of intertidal organisms along the coast of the states of michoacan and guerrero mexico measurements of the vertical extent of mortality at ten sites provided estimates of the magnitude of the vertical component of deformation along the coast within the affected area uplift ranged from about 12 centimeters to about 1 meter and no subsidence was observed the observations are consistent with models of the tectonic deformation that results from buried slip on a shallow dipping underthrust fault

the primitive matrix components of the unique carbonaceous chondrite acfer 094 a tem study the mineralogical and chemical characteristics of the fine grained matrix 53 m of the unique primitive carbonaceous chondrite acfer 094 have been investigated in detail by scanning electron microscopy sem and analytical transmission electron microscopy atem generally the fine grained matrix represents a highly unequilibrated assemblage of an amorphous material small forsteritic olivines 200 300 nm low ca pyroxenes 300 400 nm and fe ni sulfides 100 300 nm the matrix is basically unaffected by secondary processes only minor amounts of serpentine and ferrihydrite as products of hydrous alteration are present texturally the amorphous material acts as a groundmass to olivines pyroxenes and sulfides mostly exhibiting rounded or elongated morphologies only very few clastic mineral grains have been found the texture and chemical composition of the amorphous material are consistent with an origin by disequilibrium condensation in either the cooling solar nebula or a circumstellar environment as such the amorphous material may be considered as a possible precursor of matrix materials in other types of chondrites the non clastic matrix olivines fo98 99 and pyroxenes en97 100 are suggested to have formed either by condensation in the solar nebula under highly oxidizing conditions or by recrystallization from the amorphous material the formation of these grains by fragmentation of chondrule components is unlikely due to chemical and microstructural reasons rapid cooling caused the observed intergrowths of clino orthoenstatite in the mg rich matrix pyroxenes although some similarities exist comparing the fine grained matrix of acfer 094 with the matrices of the unequilibrated c03 chondrite alha77307 and the unique type 3 chondrite kakangari acfer 094 remains unique since it contains the highest measured concentrations of circumstellar sic and the second highest of diamond highest is orgueil it seems reasonable to suggested that at least parts of the amorphous material in the fine grained matrix may be of circumstellar origin

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

origin of iron rich olivine in the matrices of type 3 ordinary chondrites an experimental study in order to understand the origin of iron rich olivine in the matrices of type 3 ordinary chondrites the reaction of metallic iron and enstatite with and without forsterite and sio2 has been experimentally reproduced at temperatures between 1150 and 800 c and po2 between 10 11 and 10 16 atm between the iqf and mw buffers the olivine produced ranges from fo58 to fo34 and this composition does not change significantly with temperature and time of the runs the magnesian olivine which forms does become more magnesian with increasing forsterite enstatite ratio of the starting materials iron rich olivine fo 35 cannot be formed by the reaction of enstatite and metallic iron with or without forsterite as starting materials but it can be formed in the presence of free silica the composition of olivine becomes more iron rich with increasing silica enstatite ratio the compositional range of olivine formed from each mixture is 25 30 mole fo regardless of the temperature composition mineral assemblage and run duration from these experimental results two possibilities suggested for the origin of the iron rich olivine in the matrices of type 3 ordinary chondrites 1 free silica must have been present if the iron rich olivine was formed by solid state reactions under oxidizing condition in the solar nebula 2 reaction of silicon rich gas with metallic iron took place under oxidizing condition in the solar nebula though it is difficult to define which alternative was dominant the formation of free silica or silicon rich gas may be a result of fractional condensation this is possible if there is a reaction relation between forsterite and gas to produce enstatite the suggested fractional condensation is supported by the fact that the compositions of the fine grained matrices of type 3 ordinary chondrites are more silica rich than the bulk compositions of the chondrites though it is not known whether such conditions were established all over the nebula or locally in the nebula both fractionation and more oxidizing conditions than the average solar nebula are required for the formation of matrix olivine