shear strength of compacted soil under infiltration condition landslides in residual soil slopes are commonly induced by rainfall infiltration these residual soils are typically in an unsaturated state with negative pore water pressures or matric suctions since the groundwater tables in steep slopes are often deep the net normal and shear stresses of the soil remain essentially constant during rainwater infiltration into the slope failure of the slope during rainfall can be primarily associated with the decrease in the matric suction of the soil the objective of the study was to investigate the strength and deformation characteristics of a residual soil of the bukit timah granitic formation during infiltration that leads to slope failure there were two modified direct shear apparatuses used one apparatus was used for the determination of shear strength under controlled suction conditions while the other apparatus was used for shearing infiltration tests the shearing infiltration test results were compared with the shear strength values obtained from the shearing tests under constant suction the shearing infiltration test results indicate a close relationship between the decreasing matric suction and the increasing displacement rate of the soil specimen at the initial part of the infiltration process there is a rapid reduction in matric suction that is accompanied by little movement in the soil when failure of the soil is imminent the soil movement will accelerate

major element fractionation in chondrites by distillation in the accretion disk of a t tauri sun redistribution or loss of batches of condensate from a cooling protosolar nebula is generally thought to have led to the formation of the chemical groups of chondrites this demands a nebula hot enough for silicate vaporization over 1 3 au the region where chondrites formed alternatively heating of a protosolar accretion disk may have been confined to an annular zone at its inner edge 0 06 au from the protosun most infalling matter was accreted by the protosun but a proportion was heated and carried outwards by an x wind shu et al 1996 1997 proposed that larger objects such as chondrules and calcium aluminum rich inclusions cais were returned to the disk at asteroidal distances by sedimentation from the x wind fine dust and gas were lost to space the model implies that solids were not lost from the cold disk the chemical compositions of the chondrite groups were produced by mixing different proportions of cais and chondrules with disk solids of ci composition heating at the inner edge of the disk was accompanied by particle irradiation which synthesized nuclides including 26al the x wind model can produce cais not chondrules and allows survival of presolar grains 0 06 au from the protosun normalization to al and ci indicates that non carbonaceous chondrites may be disk material that gained a si and mg enriched fraction carbonaceous chondrites are different they appear to be ci that lost lithophile elements more volatile than ca five carbonaceous chondrite groups also lost ni and fe but the ch group gained siderophiles elemental loss from ci is incompatible with the x wind model silicon and ci normalization confirms that the cm co ck and cv groups may be ci that gained refractories as cais the si mg rich fraction may have formed by selective vaporization followed by precipitation on grains in the x wind this fractional distillation mechanism can account for lithophile element abundances in non carbonaceous chondrite groups but an additional process is required for the loss of ca and mn in the el group and for fractionated siderophile abundances in the h l and ll groups heated and recycled fractions were not homogenized across the disk so the chondrite groups were established in a single cycle of enhanced protosolar activity in lt 104 years the time for a millimeter sized particle to drift into the sun from 2 to 3 au due to gas drag

partition coefficients for calcic plagioclase implications for archean anorthosites by the use of a multiple aliquot technique combined with statistical calculations to overcome effects of alteration and contamination we have determined partition coefficients d s for rare earth elements rees between natural high ca plagioclase megacrysts and their basaltic matrices some of the basalts that we investigated are shown experimentally to crystallize only high ca plagioclase over approximately a 20 30 c temperature interval below the liquidus the ree d s agree well with experimentally determined values and predict equilibrium melts for archean anorthosites that agree well with coeval basaltic flows and dikes furthermore the d s appear to be valid for both tholeiitic and alkali basalts over a range of mg numbers 34 58 and ree concentrations la from 3 50 ppm similarly calculated d s for co sc cr rb sr cs ba hf ta and th also predict equilibrium melts for anorthosites that agree reasonably well with coeval basaltic flows and dikes the apparent values for co sc and ta seem good to better than 50 whereas the standard deviations for rb and th are equal to their means making the d s of questionable value the others are useful probably to within a factor of 2 experimental studies of the d for total fe as feot indicate a value of about 04 at an oxygen fugacity slightly below that of the qfm buffer a by product of the feot experiments was the experimental d s for mgo tio2 and k2o which could be compared with the d s from natural assemblages from the d s that were determined we suggest that plagioclase megacrysts in the bad vermilion lake anorthosite were in equilibrium with melts having the composition of tholeiitic basalts at an oxygen fugacity slightly below the qfm buffer the predicted melts have an feot content of about 13 k2o of about 15 tio2 of about 1 3 a chondrite normalized ree pattern that is nearly flat at 10 to 20 chondrites with a slight depletion of lrees other incompatible trace elements at 10 to 20 chondrites and cr and co at 0 01 to 0 1 chondrites this range of compositions is essentially identical to the tholeiitic flows and dikes in archean greenstone belts we therefore suggest that the moderately fe rich tholeiites that are hosts to plagioclase megacrysts in greenstone belts form the parental melts for megacrysts which make up the bad vermilion lake anorthositic complex and probably other similar archean anorthositic complexes

instabilities on moraine slopes induced by loss of suction a case history in comparison with saturated conditions negative pore water pressures arising from partial saturation increase the available shear strength on a potential slip surface this additional contribution is lost progressively during infiltration of rainfall leading to instabilities sometimes before full saturation is reached in such cases reliable prediction of the safety factor may be achieved by taking the suction history of the soil into account a combination of field and laboratory tests was carried out recently to investigate the triggering effect of rainfall on shallow slips in alpine moraine slopes the problem is complicated by the strong heterogeneity of these soils with particle sizes varying from silts to boulders the data highlight the influence of suction on the peak shear strength and allow for the calibration of simple models which take into account the dependence of shear strength on the saturation degree an infinite slope stability analysis is performed the results are compared wit

demonstration of ree fractionation among individual chondrules from the allende cv3 chondrite abstract abundances of ree ba sr rb k mg and ca were determined by precise mass spectrometric isotope dilution techniques for 24 chondrules from the allende cv3 chondrite the ree abundances are 2 5 10 ci for barred olivine chondrules 2 8 ci for porphyritic and nonporphyritic pyroxene chondrules 0 15 4 ci for porphyritic olivine and porphyritic olivine pyroxene chondrules and are more or less similarly fractionated general ree fractionations and large up to 170 anomalies of ce eu and yb occur in all chondrule types particularly for barred olivine and pyroxene rich chondrules positive correlations of ree with the moderately volatile elements k and rb as well as other refractory elements ca sr and ba are independent of textural type and major chemical compositions each type of chondrule has large and systematic abundance variations of k and rb but shows a constant k rb ratio close to that of cis from these results the following constraints on the chemical characteristics of precursors and chondrule forming events are suggested 1 vaporization loss of alkalis accompanied by k rb fractionation did not occur during chondrule formation melting events 2 elemental abundances were basically established prior to melting events by accretion of alkali free components and alkali bearing refractory precursors with fractionated ree 3 gas solid or liquid processes yielding ree fractionations took place during the formation of refractory precursors

al rich chondrules from the ybbsitz h4 chondrite evidence for formation by collision and splashing three al rich chondrules al2o3 10 wt from the h4 chondrite ybbsitz were chemically and mineralogically studied all three clearly crystallized from molten droplets as individual objects they consist predominantly of olivine spinel and a feldspar rich mesostasis the three al rich chondrules have high concentrations of incompatible elements the rare earth element patterns are fractionated with enrichment of light rare earths and a strong positive eu anomaly this type of fractionated refractory element pattern is indicative of igneous processes ca al rich inclusions from carbonaceous chondrites also show high enrichments in refractory elements their patterns are however either flat or fractionated according to variable volatilities of refractory elements in the solar nebula e g yb anomaly the high level of refractory siderophiles observed in ca al rich inclusions from carbonaceous chondrites is not found in the al rich chondrules we therefore conclude that the al rich ybbsitz chondrules formed by different processes than the ca al rich inclusions from carbonaceous chondrites melting of inhomogeneous precursors generally assumed for the formation of ferromagnesian chondrules is also unlikely to produce such extreme compositions the possibility that metamorphism is the cause of the high content of incompatible elements can be excluded we therefore propose a new model for the formation of the al rich chondrules they may have formed by collisions of partly molten ferromagnesian chondrules with other objects chondrules during this process al rich melt fractions residual liquids may be ejected and form independent al rich chondrules this model explains the high enrichment and the fractionated patterns of incompatible elements in al rich chondrules as well as their generally much smaller sizes compared with ferromagnesian chondrules the eu anomaly is probably due to diffusive exchange of eu between matrix and the al rich chondrules eu is decoupled from the other ree in many ferromagnesian chondrules of equilibrated ordinary chondrites including three ferromagnesian chondrules from ybbsitz analyzed in this study

al rich objects in ordinary chondrites related origin of carbonaceous and ordinary chondrites and their constituents ca al rich inclusions cais common constituents of carbonaceous chondrites have been studied extensively because they contain refractory high temperature minerals suggesting that they formed at high temperatures during the early history of the solar system few cais have previously been discovered in ordinary chondrites here we describe 169 al rich objects arbitrarily defined as having 10 wt al2o3 from 24 types 3 and 4 ordinary chondrites five regolith breccias containing unequilibrated material the unique meteorite kakangari and a few types 5 and 6 ordinary chondrites based on shape and texture we divide al rich objects into chondrules round with igneous textures irregularly shaped inclusions similar to type f and spinel rich complex cais and fragments probably fragments of al rich chondrules and inclusions for descriptive purposes we further subdivide al rich chondrules into compositional subgroups although they are entirely transitional conclusions 1 a al rich chondrules and irregularly shaped inclusions and fragments are wide spread albeit rare constituents of ordinary chondrites and are similar to cais except the coarse grained ones in carbonaceous chondrites thus providing strong support for a related origin of ordinary and carbonaceous chondrites and their constituents 2 b al rich chondrules formed as independent freely floating molten droplets and cooled rather rapidly 3 c al rich chondrules like the common mg fe rich chondrules formed by melting of millimeter to submillimeter sized dust balls in the case of al rich chondrules the dust balls consisted largely of mixtures of variable amounts of at least two solid precursor materials one refractory rich and the other volatile rich phases which we interpret as unmelted relicts in some of these objects support this model 4 d the wide ranges in bulk compositions of al rich chondrules from refractory rich to volatile rich ones yet complete transition between them and the existence of chondrules transitional in composition between the al rich and common mg fe rich chondrules of ordinary chondrites suggest that all chondrules formed by related processes differences in bulk composition result from mixing of different proportions of refractory volatile and mg fe rich and other solid precursor materials into dust balls which were then melted 5 e most irregularly shaped inclusions show no indication of a once molten origin secondary alteration has probably changed the original mineral assemblage mainly volatile rich materials entered the refractory objects as a gas reacted with the constituents and produced secondary phases rims probably formed both by decomposition and reaction with solar gas as well as by accretion 6 f coarse grained inclusions as found in allende were not observed in ordinary chondrites

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

live iron 60 in the early solar system isotopic analyses of nickel in samples from the differentiated meteorite chervony kut revealed the presence of relative excesses of 60ni ranging from 2 4 up to 50 parts per 104 these isotopic excesses are from the decay of the now extinct short lived nuclide 60fe and provide clear evidence for the existence of 60fe over large scales in the early solar system not only was 60fe present at the time of melting and differentiation that is fe ni fractionation of the parent body of chervony kut but also later at the time when basaltic magma solidified at or near the surface of the planetesimal the inferred abundance of 60fe suggests that its decay alone could have provided sufficient heat to melt small diameters of several hundred kilometers planetary bodies shortly after their accretion

extensive impact melting on the h chondrite parent asteroid during the cataclysmic bombardment of the early solar system evidence from the achondritic meteorite dar al gani 896 dag 896 is an olivine rich microporphyritic rock of komatiitic composition both the olivine composition fa 17 5 2 1 mn mg 0 0061 and the bulk oxygen isotopic composition delta 17 o 2 55 delta 18 o 3 50 indicate that dag 896 is a sample of the h chondrite parent body the bulk chemistry shows an h chondritic distribution of lithophile elements whereas chalcophile and siderophile elements are strongly depleted indicating formation through whole rock melting or nearly so of h chondrite material nearly complete loss of the metal plus sulfide component and crystallization without significant igneous fractionation superheated severely shocked chondritic relics similar to10 vol typically in the form of corroded lithic fragments 100 mum in size intimately distributed within the igneous lithology indicate that melting was triggered by a highly energetic impact which possibly induced shock pressures of similar to80 100 gpa the relatively young 3 704 0 035 ga ar 40 ar 39 crystallization age is consistent with the impact melting origin as magmatism in the asteroid belt was active only in the first hundred million years of solar system history 1ased on textural data and thermodynamic crystallization modelling we infer that dag 896 crystallized from a liquidus temperature of similar to1630degreesc under relatively slow cooling rates similar to10degreesc h 1 to 1300degreesc before quenching the two stage cooling history indicates that a reasonable formation environment might be a dike intruding cooler basement below a crater floor metal silicate fractionation may have been accomplished at least at the centimeter scale of the studied meteorite sample through differential acceleration of immiscible liquids of different density during the intense flow regimes associated with the excavation and modification stages of the cratering mechanism alternatively dag 896 may represent a surface sample of a differentiated melt body at the floor of an impact crater as gravitational settling appears to be an effective process at the surface of a chondritic parent asteroid for metal particles 1 to 10 mm in size typically observed in partially differentiated impact melt rocks stokes law indicates a settling velocity 1 in h 1 during the first few hours of crystallization on asteroidal bodies of 25 kin radius the similar to3 7 ga age of dag 896 nearly overlaps with the slightly older resetting ages of h chondrites all impact melts available from the literature indicating that the h chondrite parent asteroid underwent extensive impact melting at the enduring of the cataclysmic bombardment of the early solar system such an age overlap may also indicate early disruption of the initial h chondrite parent asteroid the close similarity between the bulk composition and degassing age of dag 896 and silicate inclusions in he iron meteorites is further evidence in support of a common origin by impact melting and metal silicate segregation on the h chondrite parent asteroid our new high precision oxygen isotopic measurements of h chondrites delta 17 o 0 77 0 04 should be extended to iies to verify this possible petrogenetic link

an ion microprobe study of the intra crystalline behavior of ree and selected trace elements in pyroxene from mare basalts with different cooling and crystallization histories abstract to study the effects of crystallization sequence and rate on trace element zoning characteristics of pyroxenes we used combined electron microprobe ion microprobe techniques on four nearly isochemical apollo 12 and 15 pigeonite basalts with different cooling rates and crystallization histories major and minor element zoning characteristics are nearly identical to those reported in the literature all the pyroxenes have similar chondrite normalized ree patterns negative eu anomalies positive slopes as defined by yb ce and slopes of ree patterns from ce to sm much steeper than from gd to yb the characteristics of the ree patterns of pigeonite and augite can be rationalized in terms of ree size and charge and m2 site characteristics numerous ree and other trace element v sr zr na sc cr zoning characteristics can be correlated with quadrilateral composition the total ree abundances increase with increasing ca in the m2 site and indicate that the distribution coefficients of ree between pyroxene and melt vary systematically with the wo component the total ree abundances also increase with decreasing mg mg fe and increasing al prior to plagioclase crystallization the eu anomaly in pyroxene is not substantially affected by plagioclase crystallization because eu3 is effectively partitioned into pyroxene relative to eu2 eu 2 eu 3 03 in pigeonite and the plagioclase effect is diluted by the low eu distribution coefficient for the more abundant pyroxene the cr and v components behave similarly in that cr and v decrease with increasing ti al in basalt sample 15058 and decrease with crystallization and at similar ti al na and sc increase in abundance from pigeonite to augite with similar ti al in both 15058 and 15499 in 15058 na decreases coherently with increasing ti al whereas sc shows a limited variability sr and zr in 15058 are somewhat more enriched in the augite with low ti al relative to pigeonite the augite does not become enriched in zr or sr until the pyroxene has high ti al and low mg mg fe in 15499 sr and zr show slight enrichment in augite relative to pigeonite these trace element zoning characteristics in pyroxene and the partitioning of trace elements between pyroxene and the melt are intimately related to the interplay among the efficiency of the crystallization process the kinetics at the crystal melt interface the kinetics of plagioclase nucleation and the characteristics of the crystal chemical substitutions within both the pyroxene and the associated crystallizing phases i e plagioclase

highly fractionated ree in the hedjaz l chondrite implications for nebular and planetary processes abundances of ree sr rb k ca and mg in two whole rock fragments two lithic fragments and three chondrules of the hedjaz l3 chondrite were determined by isotope dilution mass spectrometry one whole rock fragment shows a step pattern with the light ree enriched indicating that the meteorite contains components with highly fractionated ree abundances the chondrules pp bo and one unknown type show variable 0 8 2 ci ree abundances and almost flat ree patterns with minor irregularities of ce eu and yb anomalous ree patterns were identified for two light colored lithic fragments a pyroxene rich glass bearing subrounded clast i has low ree abundances 0 3 0 8 ci together with depletion of other lithophiles ca al sr na and k it shows a light ree enhanced pattern with positive anomalies of ce eu and yb this is a new ree pattern reported for lithic clasts from ordinary chondrites it is suggested that the clast formed through melting processes possibly under planetary conditions from the condensates either from a later stage nebular gas or from gas vaporized from dust the second clast ii ca 1 1 1 9 consists mainly of coarse grained olivine minor pyroxene and plagioclase and trace amounts of glass it shows an igneous texture with shock features it has a strong positive correlation of plagiophile elements ca sr and eu but heterogeneous distributions of common ree from portion to portion one of the chips indicates a remarkable ree fractionation lree 40 hree 1 7 ci similar to that of group ii cai s of carbonaceous chondrites this is the first identification of group ii ree pattern in lithic clasts from ordinary chondrites it is suggested that the clast had formed by shock induced melting of an inhomogeneous cv like precursor assemblage carrying high temperature nebular ree components on a grand parent body and was then incorporated into the hedjaz meteorite parent body the presence of impact related products with highly fractionated ree components in a chondritic breccia indicates the existence of related physico chemical conditions in the formation of chondrules clasts and their precursors with that of cai s

a survey of clasts and large chondrules in ordinary chondrites we report the results of a survey of clasts and large 5 mm chondrules macrochondrules within the 833 ordinary chondrites of the natural history museum collection thirty six macrochondrules and 24 clasts were identified and studied macrochondrules have textures and mineral assemblages like normal chondrules and so share a common origin clasts show evidence for fracturing from larger bodies and can be classified as either 1 chemically fractionated if they have major and trace element compositions differing substantially from most chondrules and clasts 2 impact melt clasts if they have microporphyritic textures and signs that indicate they are derived from shock melted chondritic material 3 microporhyritic clasts if they are similar to the last category but lack evidence for derivation through shock melting or 4 indeterminate clasts forming a diverse class that includes all those clasts that do not fit into the other categories

postfailure mechanics of landslides laboratory investigation of flowslides in pyroclastic soils of all landslides subaerial flowslides are the most dangerous according to the literature flowslides in saturated granular deposits are caused by static liquefaction induced by loss of stability however the catastrophic flowslides that occurred on steep slopes in campania southern italy in 1998 1999 and 2005 were triggered by rainwater infiltration into shallow deposits of pyroclastic soils which were initially unsaturated starting from the experience collected during the investigations of some of these landslides the writers consider flowslide evolution as a result of a mechanical chain process characterized by saturation increase due to rainwater infiltration mechanical degradation volumetric collapse and static liquefaction culminating in complete fluidization of the soil in the paper this chain process is investigated through wetting tests both in suction controlled triaxial apparatuses and in a well equipped small scale slope model

composition and origin of nuevo laredo trend eucrites new bulk rock analyses are reported for the eucritic meteorites alha81001 lakangaon and nuevo laredo alha81001 resembles ibitira as both have far lower concentrations of na than any other eucrite lakangaon and nuevo laredo are the two most ferroan low mgfe of all eucrites monomict eucrites have previously been divided into three geochemical classes a main group and the nuevo laredo and stannern trends the nuevo laredo trend which is characterized by limited variations of incompatible element contents despite considerable variations in mg mg fe ratio and v content clearly formed out of melt s undergoing fractional crystallization probably as partial cumulates the less distinctive main group eucrites are often assumed to be primary basalts geochemically but one step equilibrium partial melting removed from the bulk composition of the eucrite parent asteroid this partial melting model seems more appropriate for the stannern trend which is characterized by moderate high mg mg fe despite moderate high incompatible element contents our new data and a review of literature data suggest that most of the so called main group eucrites actually belong to the nuevo laredo trend while few if any belong to the stannern trend or any other partial melting trend the nuevo laredo trend may be part of a series of fractional crystallization products that began with orthopyroxenite cumulates diogenites the bulk mgo mgo feo ratio of the eucrite parent asteroid is generally estimated at 0 67 by assuming that typical eucrites are primary basalts but if typical eucrites are diogenite comagmatic fractional crystallization products the bulk mgo mgo feo of the parent asteroid must be considerably higher probably about 0 81

radiometric ages of basaltic achondrites and their relation to the early history of the solar system pbpb mineral isochrons were determined for three cumulate eucrites moama moore county and serra de mage and three noncumulate eucrites nuevo laredo bouvante and stannern two noncumulate eucrites bereba and cachari show disturbed pb isotope patterns the mineral isochron ages of cumulate eucrites range from 4 40 ga to 4 48 ga the latter is the age of moore county 4 484 0 019 ga which was also dated by the smnd method at 4 456 0 025 ga nuevo laredo and bouvante give the same pb pb age 4 514 0 015 ga and 4 510 0 004 ga respectively the pb isochron of stannern corresponds to 4 128 0 016 ga which is a reequilibration age both cachari and bereba show evidence of isotope resetting at about 4 ga a pb pb multicotrelation approach is introduced and applied to the data the younger ages of the cumulate eucrites preclude their formation by fractional crystallization from the melts that produced the noncumulate eucrites the 1 of the source of the cumulate eucrites is 14 whereas that of the source of the noncumulate eucrites is 150 this large difference in 1 values suggests that eucrites were derived from separate planetesimals or from a single heterogeneous layered parent body

a short duration of chondrule formation in the solar nebula evidence from 26al in semarkona ferromagnesian chondrules abstract the 26 al 26 mg systems of five ferromagnesian chondrules from the least metamorphosed ordinary chondrite semarkona ll3 0 were studied using a secondary ion mass spectrometer their glass or plagioclase portions contain excesses of 26 mg and in two chondrules the 26 mg excesses are well correlated with 27 al 24 mg which demonstrates the in situ decay of 26 al the initial 26 al 27 al ratios in these chondrules obtained from the slope of isochrons show a narrow range of between 6 10 6 and 9 10 6 indicating their short formation duration of less than 1 my if the solar nebula was initially homogeneous in al isotopes the chondrule formation ages are 2 my younger than those of cais our results based on the study of the least metamorphosed uoc are consistent with the previous studies on al rich chondrules that the chondrule formation started at least 2 my after cais alternatively the older records before 2 my were erased by chondrule recycling process it further suggests that the young apparent ages 3 to 5 my after cais for chondrules in type 3 4 uocs are due to the disturbance of the 26 al 26 mg system possibly during parent body metamorphism the result is not consistent with the extended nebular time scale of 5 my and the chondrule formation by planetary processes the ni isotopic analysis of the feo rich olivines in a type ii chondrule in semarkona did not show any detectable excess 60 ni in spite of their high fe ni ratios the upper limit of the initial 60 fe 56 fe ratio of the solar system was estimated to be 3 4 10 7 which is consistent with the previous estimate 0 2 1 9 10 7 from eucrites this result confirms that the 60 ni excess previously observed from cais was not due to the decay of the short lived nuclide 60 fe but a ni isotopic anomaly of nucleosynthetic origin

60fe 60ni systematics in the eucrite parent body a case study of bouvante and juvinas abstract eucrites are basaltic meteorites that cooled rapidly but are in many instances thermally metamorphosed and impact brecciated the exact timing of these events remains unclear in this study ni isotopic compositions and fe ni elemental ratios are presented for two non cumulate eucrites bouvante and juvinas including mineral separates from the latter the samples are characterized by variable well resolved 60 ni excesses consistent with the former presence of live 60 fe t 1 2 2 62 ma at the time of eucrite crystallization a significant fraction of ni with a terrestrial like composition appears to be surface correlated this ni may be the product of terrestrial contamination or was introduced by a chondritic impactor during brecciation altogether the data provide evidence for a complex and probably multi stage history of fe and or ni redistribution which impedes the interpretation of the chronological data

large silica rich igneous textured inclusions in the buzzard coulee chondrite condensates differentiates or impact melts we studied three large 2 4 mm diameter igneous textured inclusions in the buzzard coulee h4 chondrite using microanalytical techniques olm sem empa sims to better elucidate the origins of igneous inclusions in ordinary chondrites the inclusions are clasts that come in two varieties 1 white inclusions bz 1 and bz 2 represent a nearly holocrystalline assemblage of low ca and high ca pyroxene 63 66 area and cristobalite 33 36 and 2 tan inclusion bz 3 is glass rich approximately 60 with low ca and high ca pyroxene phenocrysts the bulk compositions of the inclusions determined by modal reconstruction are all sio2 rich approximately 67 wt for bz 1 and bz 2 approximately 62 for bz 3 but bz 3 is enriched in incompatible elements e g ree approximately 4 5 ci abundances whereas bz 2 and bz 1 are depleted in those elements that are most incompatible in pyroxene e g la ho approximately 0 15 0 4 ci abundances these bulk compositions do not resemble what one would expect for partial or complete shock melting of a chondritic precursor and show no evidence for overall volatility control we infer that the inclusions originated through igneous differentiation and feo reduction with bz 3 forming as an andesitic partial melt approximately 30 40 partial melting of an h chondrite precursor and bz 1 and bz 2 forming as pyroxene cristobalite cumulates from an si rich melt we suggest that both types of melts experienced a period of transit through a cold low pressure space environment in which cooling feo reduction and interaction with a vapor occurred melts may have been lofted into space by excavation or splashing during collisions or by pyroclastic volcanism our results indicate intriguing similarities between the inclusions in buzzard coulee and the silicates in some iron iie type and stony iron iva type meteorites suggesting a genetic relationship

highly siderophile elements in ureilites abstract the abundances of the highly siderophile elements hse ru pd re os ir and pt were determined by isotope dilution mass spectrometry for 22 ureilite bulk rock samples including monomict augite bearing and polymict lithologies this report adds significantly to the quantity of available pt and pd abundances in ureilites as these elements were rarely determined in previous neutron activation studies the ci normalized hse abundance patterns of all ureilites analyzed here except alha 81101 show marked depletions in the more volatile pd with ci chondrite normalized pd os ratios excluding alha 81101 averaging 0 19 0 23 2 this value is too low to be directly derived from any known chondrite group instead the hse bulk rock abundances and hse interelement ratios in ureilites can be understood as physical mixtures of two end member compositions one component best represented by sample alha 78019 is characterized by superchondritic abundances of refractory hse rhse ru re os ir and pt but subchondritic pd rhse and is consistent with residual metal after extraction of a s bearing metallic partial melt from carbonaceous chondrite like precursor materials the other component best represented by sample alha 81101 is rhse poor and has hse abundances in chondritic proportions the genesis of the second component is unclear it could represent regions within the ureilite parent body upb in which metallic phases were completely molten and partially drained or it might represent chondritic contamination that was added during disruption and brecciation of the upb removal of carbon rich melts does not seem to play an important role in ureilite petrogenesis removal of such melts would quickly deplete the ureilite precursors in re os and as au which is inconsistent with measured osmium isotope abundances and also with literature as au data for the ureilites removal of 26 al during silicate melting may have acted as a switch that turned off further metal extraction from ureilite source regions

brecciation among 2280 ordinary chondrites constraints on the evolution of their parent bodies abstract after accretion of meteorite parent bodies larger and smaller collisions have led to significant modifications of these bodies involved processes include excavation of material thermal metamorphism melting mixing of different materials re accretion and re lithification all these processes can be repeated several times in this study polished thin sections pts of 2280 chondrites 1193 h 947 l and 140 ll chondrites were investigated in order to obtain the abundance of brecciated rocks among the ordinary chondrites in addition we have determined the abundance and characteristics of shock vein bearing h l and ll chondrites and of impact melt rock clasts we also recognized xenolithic components based on o isotope studies noble gas data were considered in order to detect regolith breccias and to discuss late impact histories the investigation of 2280 samples shows that 23 276 of 1193 of the h chondrites 23 220 of 947 of the l chondrites and 79 110 of 140 of the ll chondrites are brecciated considering the heavily brecciated ll chondrites in 63 of the 140 chondrites 45 shock veins were clearly detected 57 of these 63 chondrites are brecciated rocks the investigation of the h and l chondrites has shown that about 26 310 of 1193 of the h chondrites and 40 379 of 947 of the l chondrites contain shock veins in our data set 20 of the h chondrites and 8 3 of the ll chondrites but only 3 0 of the l chondrites contain solar noble gases remarkably about 62 of all brecciated h chondrites with noble gases analyzed contain solar noble gases compared to only around 11 and 10 of the brecciated l and ll chondrites respectively the identification of xenolithic clasts e g ci cm and ureilite like lithologies in primitive type 3 chondrites indicates simultaneous accretion of clasts and chondrules these clasts must have been formed early within the first 2 ma on subsequently destroyed precursor first generation parent bodies the formation of complex breccias witnesses the collisions between asteroids of very different lithologies and heritage although the onion shell configuration of primordial parent bodies is necessary in order to form the chondrites with different degrees of metamorphic overprint petrologic types 3 6 subsequent catastrophic fragmentation and reassembly to form asteroids with a rubble pile structure are required to explain certain features discussed in this work however distinct peaks in the cosmic ray exposure age distributions indicate that not too many impacts in the last 100 ma were responsible to deliver the majority of the ordinary chondritic meteoroids to earth yet this certainly does not tell anything about the number of last generation parent bodies that exist in the asteroid belt since s type asteroids are the most abundant type of asteroid in the inner main belt and thought to be the parent bodies of ordinary chondrites

petrogenesis of mesosiderites i origin of mafic lithologies and comparison with basaltic achondrites abstract new petrologic and trace element data on basaltic and gabbroic clasts in mesosiderites and basaltic achondrites combined with existing petrologic and trace element data have served as a basis for interpretation of the petrogenesis of mesosiderite clasts compared with the basaltic achondrites the mesosiderite basaltic and gabbroic clasts contain more abundant modal tridymite and merrillite and more commonly contain augite as a late magmatic phase their pyroxenes tend to be more mgo rich and have lower fe mn ratios which are positively correlated with the fe mg ratio some of the mesosiderite basaltic and gabbroic clasts contain xenocrystic plagioclase the basaltic clasts commonly show super chondritic eu sm ratios and slight lree depletions the cumulate gabbro clasts are extremely depleted in lil have very high eu sm ratios and high lu sm ratios all of these features can be explained by a model in which the mafic lithologies of mesosiderites were formed by remelting of a mixed basalt cumulate gabbro metal source region near the parent body surface reducing agents p c s from the metallic fraction reduce feo out of the silicate melt and result in the positive correlation of fe mn with fe mg observed in pyroxene analyses and the modal abundances of tridymite merrillite and augite xenocrystic plagioclase is a natural consequence of remelting a cumulate gabbro rich source as are the unique ree patterns observed

age and isotopic relationships among the angrites lewis cliff 86010 and angra dos reis results of a wide ranging isotopic investigation of the unique antarctican angrite lew 86010 lew are presented together with a reassessment of the type angrite angra dos reis ador the principal objectives of this study are to obtain precise radiometric ages initial sr isotopic compositions and to search for the erstwhile presence of the short lived nuclei 146sm and 26al via their daughter products the isotopic compositions of sm u ca and ti were also measured this allows a detailed appraisal to be made of the relations between and the geneology of these two angrites lew proves to be severely contaminated with modern terrestrial pb which is shown to result from terrestrial weathering nevertheless concordant pb pb model ages of pyroxene separates were obtained 2 4 55784 52 ga for lew and 4 55780 42 ga for ador uranium isotopic compositions are normal within error the inferred initial pb isotopic composition is within error of primordial pb as defined by canon diablo troilite because of the extreme upb ratios of both angrites this places an upper limit of 2 ma on the time between volatile element loss of the angrite parent body or its precursor planetesimals and the final crystallization of the angrites as differentiates initial 87sr86sr ratios were found to be indistinguishable in lew ador and the cumulate eucrite moore county the derived initial 87sr86sr for all three meteorites is 0 698970 15 2 a 147sm 143nd isochron for lew was obtained yielding an age of 4 553 34 ga with an initial 143nd144nd of 0 506682 49 2 146sm142nd isotope systematics were also measured anomalies on 142nd arising from extinct 146sm were clearly resolved resulting in an initial 146sm144sm of 0 0071 17 with nd142 2 57 0 62 at the time of isotopic closure both of these sm nd methods imply derivation of lew from a reservoir with chondritic smnd ratio they are also quite consistent with the previously reported systematics for ador overall the age and isotopic similarities between lew and ador are striking it suggests almost simultaneous production on the same asteroid even though recent experimental studies imply that the two are not comagmatic calcium and titanium do not exhibit enrichments in the n rich isotopes in contrast to cais making it unlikely that the angrite parent body is inherently rich in early condensates from the solar nebula no evidence was found for live 26al in lew when combined with the pb pb age and initial 87sr86sr data this firmly excludes 26al being an important heat source in the early solar system heat supplied for for example 1 the differentiation of the angrite and eucrite parent bodies and 2 metamorphism of the chondrite parent bodies must come from some other source the debate over live vs extinct 26al in the earliest solar system remains unresolved by this new data from lew however both the angrite and eucrite parent bodies have extremely low rbsr and high upb ratios compared to the solar nebula therefore the common initial 87sr86sr of 0 698970 can be firmly associated with the u pb angrite age above and the formation of both bodies this enables an absolute chronology of the early solar system to be established based upon 87sr86sr differences the oldest cais are a minimum of 11 4 ma older than the angrites i e 4 569 5 ga the age and isotopic constraints are discussed with respect to current collapse condensation and accretion timescales calculated for the solar nebula

puxe dating of eucrites abstract we report the results of xe analyses of the eucrites bereba cachari caldera camel donga chervony kut ibitira jonzac juvinas milbillillie moore county padvarninkai pasamonte pomozdino sioux county and vetluga and the howardite petersburg the obtained data together with data from the literature were utilized for the calculation of pu xe ages using a modified method where the concentration of the reference element nd that is used in the traditional pu xe dating is replaced by that of spallation 126 xe originating from rare earth elements the fraction of spallation 126 xe from ree in total spallation 126 xe is calculated via the ba ree ratios that are very similar in different samples of a given meteorite in comparison with the traditional pu xe dating the present method avoids problems of sampling heterogeneity and uncertainties in absolute instrument sensitivity and can be used when the concentration of nd in a sample is not known the pu xe ages for different samples of individual meteorites show good reproducibility ages of the eucrites bouvante chervony kut ibitira juvinas moore county pasamonte pca82502 pomozdino of the howardite petersburg and of the angrite lew86010 are old and most likely date the time of crystallization at 4 56 ga almost complete retention of fission xe in these meteorites is in a stark contrast with the apparent 1 retention of radiogenic 129 xe the eucrites bereba cachari caldera camel donga jonzac millbillillie neuvo laredo padvarninkai sioux county stannern and vetluga are distinctly younger this can be interpreted in different ways the ages may represent crystallization and or metamorphic ages or may simply reflect the different extent of diffusive fission xe losses during later events comparison of the pu xe ages with those from the sm nd and pb pb isotope chronometers yields in most cases a reasonable agreement in some meteorites however the pb pb chronometer appears to have been reset during secondary events while the pu xe isotope system is seen to be more resistant to such events

impact history of the hed parent body ies clarified by new 40ar 39ar analyses of four hed meteorites and one anomalous basaltic achondrite abstract we investigate the thermal impact histories of four hed meteorites one cumulate eucrite lake carnegie two brecciated basaltic eucrites camel donga millbillillie one howardite old homestead 003 and an anomalous basaltic achondrite deakin 010 we have measured eight convincing new 40ar 39ar ages for three hed meteorites laser incremental 40ar 39ar analyses of carefully separated small grains two concordant 40ar 39ar plateau ages were obtained for plagioclase separates from lake carnegie resulting in a weighted mean age of combined plateau ages of 4507 20 ma millbillillie recorded three impact events at 3722 55 ma 3579 28 ma and 3313 174 ma from plagioclase matrix and pyroxene respectively this highlights the power of the k ar system to record impacts of different magnitudes experienced by a single meteorite two aliquots from camel donga returned concordant plateau ages interpreted to represent a single significant impact event at 3693 51 ma the anomalous basaltic achondrite deakin 010 did not yield any plateau and resulted in a series of minimum apparent ages with an oldest minimum age of 3 66 ga for the largest impact recorded cosmic ray exposure ages yielded apparent 38arc ages ranging from 6 to 40 ma two clusters of ages that represent significant impacts into the hed parent body may have been identified the first high temperature event is recorded by lake carnegie and other unbrecciated eucrites at 4 5 ga and is interpreted as a mega impact although it is also possible that this age is recording magmatic crystallisation due to the similarity of published sm nd and pb pb ages additionally from statistically reliable isotopic ages provided in this study it appears that the age range of major impact heating events post 4 5 ga might be more tightly restricted 3 8 3 5 ga than previously suggested 3 4 4 1 ga however a larger dataset is required before comparison with the range of the lunar heavy bombardment is justified if hed are indeed from 4 vesta we raise the possibility that the impact at 4 5 ga might be associated with the formation of the south polar veneneia basin whereas an age at 3 7 ga may represent the formation age of either veneneia or the younger rheasilvia impact structure

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

origin of plagioclase olivine inclusions in carbonaceous chondrites plagioclase olivine inclusions pois are an abundant group of chondrule like objects with igneous textures found in carbonaceous chondrites pois consist of plagioclase olivine pyroxene and spinel and cover a wide range of compositions between type c ca al rich inclusions cais and ferromagnesian chondrules pois are distinguished from cais by the absence of melilite lack of refractory siderophile rich opaque assemblages more sodic plagioclase and abundance of olivine and aluminousenstatite rare accessory minerals including armalcolite zirconolite rutile and sapphirine are found in several pois the petrographie and chemical properties of pois indicate that they are not condensates or evaporative residues but formed by melting or partial melting of pre existing solids seven of fourteen pois contain isotopically fractionated mg and despite their textures these pois are not isotopically homogeneous spinel is the major carrier of fractionated mg in six pois the magnitude of mg isotopic fractionation fmg of spinel ranges from 8 to 11 amu among the pois but f mg is always either positive or negative within an individual pol within a single inclusion f mg of coexisting spinel is not constant but varies by up to 7 amu isotopic fractionation of mg in silicates is less common and always positive f mg 0 pyroxenes in two pois and plagioclase in a third contain isotopically heavy mg radiogenic 26 mg is rare in pois as only two inclusions show evidence of excess 26 mg with 26 mg 27 al 4 10 6 the preservation of isotopic heterogeneity in objects whose igneous textures suggest crystallization from a homogeneous melt implies that melting was incomplete allowing survival of relict phases a comparison of the essential characteristics of pois and cais suggests that the major processes leading to formation of pois including condensation dust gas fractionation aggregation of chemically and isotopically disparate materials and partial melting are common to most cais and chondrules we present a scenario for the formation of these objects and conclude that the homogeneity of the final assemblage cai poi or chondrule is primarily a reflection of the thermal history rather than the nature of precursor materials

a unique high mn fe microgabbro in the parnallee ll3 ordinary chondrite nebular mixture or planetary differentiate from a previously unrecognized planetary body the study of planetary materials in chondritic meteorites constrains the compositional diversity of materials in different nebular environments and provides information on the degree of differentiation of early planetary bodies we studied a unique microgabbro fragment from the parnallee ll3 unequilibrated ordinary chondrite the fragment which was originally identified by its ophitic to sub ophitic texture exhibits features characteristic of lunar and terrestrial tholeiitic basalts extreme compositional zoning in clinopyroxene wo 10 en 65 fs 25 to wo 15 en 2fs 83 a multiply saturated major element composition similar to mid ocean ridge basalt with 3 1 wt na 2o and 0 15 wt k 2o and uniformly enriched rare earth elements c 10 c1 a high bulkmno feo ratio 0 064 distinguishes the microgabbro from other basaltic rocks and suggests the precursor material formed or reached equilibrium in a reducing environment however the absence of fe metal and the extreme enrichment of feo up to 40 wt in late crystallizing pyroxferroite requires the last crystallization event to have occurred in a relatively oxidizing environment we suggest the microgabbro formed by partial melting in a planetary body after removal of metallic fe examination of possible planetary source materials such as alkali rich eucritic material a volatile depleted c1 carbonaceous chondrite or h group chondrite shows that multiple stage fractionation is required to produce a melt with the feo mgo ratio of the microgabbro from these materials the increasing number of planetary igneous fragments observed in unequilibrated ordinary chondrites uoc suggests the picture of uoc as primitive assemblages of unprocessed material is overly simplistic

major and trace elements of zircons from basaltic eucrites implications for the formation of zircons on the eucrite parent body abstract the major and trace elements in zircons obtained from basaltic eucrites yamato y 75011 y 792510 y 82082 asuka a 881467 juvinas and stannern were determined using an electron microprobe analyzer and a sensitive high resolution ion microprobe and the formation of zircons on the parent body was discussed the maximum sizes of zircon grains in each sample are likely to be related to its metamorphic grade the least metamorphosed basaltic eucrite y 75011 contains zircons with sizes of a few m conversely the highly metamorphosed basaltic eucrites y 792510 and a 881467 include zircons larger than 20 m the relationship between the maximum grain size and metamorphic grade suggests that the formation process of zircons is related to metamorphic events the zr hf ratios of the zircons found in this study show a wide variation 31 6 71 7 as compared to the chondritic values zr hf 32 8 34 3 and bulk basaltic eucrites 34 0 34 7 the zr hf ratios of the zircons from y 792510 and a 881467 are relatively constant whereas those of the zircons from y 82082 juvinas and stannern show large variations the rare earth element ree content in the zircons from y 792510 and a 881467 is given by la 0 1 ci and lu 1000 ci on the other hand the zircons from stannern show higher ree content la 0 1 1 ci and lu 1000 10 000 ci than those from y 792510 and a 881467 the most reliable ree data of a large zircon from a 881467 show no ce anomaly and a distinct negative eu anomaly therefore it is presumed that the zircons formed under reducing condition in which ce 3 was stable the melt compositions coexisting with the studied zircons suggest that the zircons from highly metamorphosed eucrites might react with the ree enriched melt derived from partial melting of the mesostasis region during metamorphism

quantifying the error of 2d bulk chondrule analyses using a computer model to simulate chondrules simchon bulk chondrule compositions are important to many questions in cosmochemistry however the number of available bulk chondrule data sets is still small a main reason for this is the difficulties of determining bulk chondrule compositions a commonly used technique is to obtain 2d bulk chondrule compositions from meteorite sections this technique has an error that we quantify here for the first time using a mathematical model of a chondrule called simchon the theoretically calculated errors are compared to errors that we determined from serial sectioning of eight efremovka chondrules the errors obtained from both approaches are in excellent agreement proving that our mathematical model produces reliable errors that can be assigned to 2d bulk chondrule compositions these errors allow a much better interpretation of 2d bulk chondrule data we provide a table that contains typical errors for 2d bulk compositions of porphyritic chondrules the errors are in the range of 1 30 relative this should be acceptable for many problems in cosmochemistry the effect of a chemical layering inside chondrules and the occurrence of a rim around them as well as the occurrence of opaque and other accessory phases have been studied a spreadsheet is provided that enables the calculation of errors for any desired chondrule mineral composition bo chondrules have a negligible error but it is impossible to provide reasonable error estimates for bo chondrules with an igneous rim radial pyroxene chondrules have negligible errors

crumbs from the crust of vesta achondritic cosmic spherules from the south pole water well ten glass cosmic spherules cs from the south pole water well collection were analyzed by electron microprobe nine of them have fe mn and fe mg ratios in the range typical of chondrites one of them sp37 3 along with up to six other previously analyzed cs have nonchondritic fe mn and fe mg ratios that agree well with values typical of either basaltic howardite eucrite and diogenite hed meteorites or martian basalts but not of lunar samples sp37 3 also contains an anorthite relic grain anorthite has not previously been reported in cosmic spherules but is well known in hed meteorites the much greater frequency of heds among hand sized meteorites suggests but does not prove that hed precursors are more likely for the nonchondritic spherules we estimate that hed like micrometeorites constitute 0 5 0 4 of the total population of micrometeorites in the south pole water well a fraction that translates to a flux of 1 6 0 3 x 10 8 g hed micrometeorites m 2 y the ratio of hed like objects to carbonaceous objects is about 100 times less in micrometeorites than among hand size specimens we infer that the comparative mechanical weakness of carbonaceous precursor materials tends to encourage spherule formation

post crystallization reheating and partial melting of eucrite eet90020 by impact into the hot crust of asteroid 4vesta 4 50 ga ago we performed petrologic radiometric ar ar sm nd and mn cr ages and ion microprobe studies of the basaltic eucrite eet90020 this is one of the few rare basaltic eucrites whose 39ar 40ar age has not been reset during impact bombardment on the hed parent body 4 ga ago and thus should provide a unique opportunity to study the nature of the early thermal events on its parent body presumably asteroid 4vesta hand specimen inspection shows that the rock consists of a fine grained and a coarse grained lithology microscopy indicates that the fine grained lithology has a granulitic texture with a coarser grained area and a large opaque assemblage embedded in the granulitic matrix the coarse grained lithology has an igneous subophitic texture the rock has pyroxenes similar to those in type 5 eucrites type 5 pyroxene and experienced prolonged thermal metamorphism after rapid crystallization from a near surface melt however minor mineral assemblages are unusual and suggest a complex thermal history tridymite occurs as large laths irregular crystals 1 5 gpa after the reheating event eet90020 seems to have experienced the following thermal history 1 crystallization during rapid cooling near the surface 2 some brecciation by impact 3 thermal metamorphism that produced type 5 pyroxene and 4 short reheating that caused partial melting and rapid cooling 39ar 40ar measurements show a relatively flat pattern and an age of 4 49 0 01 ga which is consistent with rapid cooling from high temperature event 4 resetting of the sm nd ages at 4 51 0 04 ga appears to be closely related to the remelting of ca phosphates rb sr data suggest rb loss from tridymite during partial melting the resetting of the mn cr age may have been related to the formation of cr ulvospinels event 4 we suggest that all these ages were reset by partial melting event 4 we further suggest that the partial melting event event 4 that reset the ages 4 50 ga ago was caused by an impact into eet90020 which was part of the hot crust of 4vesta and resulted in an increase in the temperature from the ambient temperature of 870 c to above the subsolidus temperature of eucrites of 1060 c

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

late accretion and lithification of chondritic parent bodies mg isotope studies on fragments from primitive chondrites and chondritic breccias recent results of isotopic dating studies 182hf 182w 26al 26mg and the increasing number of observed igneous and metamorphosed fragments in primitive chondrites provide strong evidence that accretion of differentiated planetesimals predates that of primitive chondrite parent bodies the primitive chondrites adrar 003 and acfer 094 contain some unusual fragments that seem to have undergone recrystallization magnesium isotope analyses reveal no detectable radiogenic 26mg in any of the studied fragments the possibility that evidence for 26al was destroyed by parent body metamorphism after formation is not likely because several other constituents of these chondrites do not show any metamorphic features since final accretion of a planetesimal must have occurred after formation of its youngest components formation of these parent bodies must thus have been relatively late i e after most 26al had decayed al mg isotope data for some igneous textured clasts granitoids and andesitic fragments within the two chondrite regolith breccias adzhi bogdo and study butte reveal also no evidence for radiogenic 26mg as calculated from the upper limits the formation of these igneous clasts the incorporation into the parent body regolith and the lithification must have occurred at least 3 8 myr andesite in study butte and 4 7 myr granitoids in adzhi bogdo after calciumaluminum rich inclusions cai formation the absence of 26mg excess in the igneous inclusions does not exclude 26al from being a heat source for planetary melting in large early formed planetesimals cooling below the closure temperature of the al mg system may be too late for any evidence for live 26al in the form of 26mg excess to be preserved thus growing evidence exists that chondritic meteorites represent the products of a complex multi stage history of accretion parent body modification disruption and re accretion

compositional differences between basaltic and gabbroic clasts in mesosiderites two gabbroic pebbles and one pebble with basaltic textural affinities from the vaca muerta mesosiderite were analyzed by instrumental neutron activation analysis and electron microprobe these analyses plus literature data reveal remarkable compositional differences between basaltic and gabbroic clasts in mesosiderites on average basaltic clasts have small 15 depletions in light relative to heavy rare earth elements rees and moderate positive eu anomalies i e h chondrite normalizedla lu 0 85 eu sm 1 30 the meanla lu andeu sm abundance ratios of gabbroic clasts are at least 3 3 smaller and 28 greater respectively intense meteoroid bombardment probably persisted until after the mesosiderite parent body had differentiated near surface mixtures of major amounts of basalt and lesser amounts of cumulate eucritic rocks were essentially totally melted and rapidly cooled accounting for the moderately fractionated ree patterns of most basaltic clasts at greater depths impact heating partially melted cumulate gabbros incompatible element rich eutectic liquids drained away creating large ree fractionations in the residual rocks these rocks cooled slowly and developed gabbroic textures

fossil records of high level of 60fe in chondrules from unequilibrated chondrites abstract the short lived now extinct nuclide sln 60fe which decays to 60ni with a half life of 2 62 ma is uniquely of stellar origin hence its solar system initial abundance yields information about the source of slns and the astrophysical environment in which the solar system was born only a few chondrules 19 from unequilibrated ordinary chondrites have reported resolved 60ni excesses using in situ secondary ion mass spectrometry implying fe 60 fe 56 0 6 10 7 in the early solar system and among these very few 3 have higher excesses implying fe 60 fe 56 7 10 7 mishra et al 2010 mishra and goswami 2014 telus et al 2012 at variance multi collector inductively coupled plasma mass spectrometer studies of bulk samples and mineral separates from differentiated meteorites angrites achondrites and chondrules suggest a low abundance of 60fe 56fe of 1 4 10 8 which would rule out the need for an external seeding of the early solar with stellar 60fe quitte et al 2011 tang and dauphas 2012 two semarkona chondrules and one efremovka chondrule analyzed in the present study have mass fractionation corrected excess of up to 75 permil and give 60fe isochrons with initial 60fe 56fe ratios of 7 8 3 7 10 7 3 8 1 6 10 7 and 2 2 1 1 10 7 2 for efremovka ch 1 semarkona ch 12 and semarkona ch j5 respectively the higher values of 60fe 56fe ratios seen in the chondrules of these least altered meteorites samples concur with and lend greater credence to the suggestion of a massive star as the source of 60fe and possibly of other short lived nuclides to the early solar system however no definitive explanation e g sample bias effects of metamorphism 60fe heterogeneity to the apparent disagreement with studies of bulk chondrules and chondrule fragments has been found

the origin of chondrules and chondrites debris from low velocity impacts between molten planetesimals we investigate the hypothesis that many chondrules are frozen droplets of spray from impact plumes launched when thin shelled largely molten planetesimals collided at low speed during accretion this scenario here dubbed splashing stems from evidence that such planetesimals intensely heated by 26al were abundant in the protoplanetary disk when chondrules were being formed approximately 2 myr after calcium aluminum rich inclusions cais and that chondrites far from sampling the earliest planetesimals are made from material that accreted later when 26al could no longer induce melting we show how splashing is reconcilable with many features of chondrules including their ages chemistry peak temperatures abundances sizes cooling rates indented shapes relict grains igneous rims and metal blebs and is also reconcilable with features that challenge the conventional view that chondrules are flash melted dust clumps particularly the high concentrations of na and feo in chondrules but also including chondrule diversity large phenocrysts macrochondrules scarcity of dust clumps and heating we speculate that type i feo poor chondrules come from planetesimals that accreted early in the reduced partially condensed hot inner nebula and that type ii feo rich chondrules come from planetesimals that accreted in a later or more distal cool nebular setting where incorporation of water ice with high 17o aided oxidation during heating we propose that multiple collisions and repeated re accretion of chondrules and other debris within restricted annular zones gave each chondrite group its distinctive properties and led to so called complementarity and metal depletion in chondrites we suggest that differentiated meteorites are numerically rare compared with chondrites because their initially plentiful molten parent bodies were mostly destroyed during chondrule formation

the geologic history of vesta inferred from combined 207pb 206pb and 40ar 39ar chronology of basaltic eucrites abstract eucrites represent samples of mafic crust of the parent body likely vesta and record a complex geologic history involving magmatism metamorphism impact processing and metasomatism for better understanding of the geologic history we present combined 207pb 206pb and 40ar 39ar chronology of four basaltic eucrites showing distinct petrologic features agoult an equilibrated eucrite with granulitic textures camel donga a brecciated equilibrated eucrite enriched in metallic iron dag 380 a partially equilibrated monomict eucrite and nwa 049 a metasomatized polymict eucrite comprising mostly unequilibrated clasts the 207pb 206pb dating in combination with the acid washing technique was applied to pyroxene rich and plagioclase rich fractions while the 40ar 39ar dating was performed mainly on plagioclase grains using the laser incremental heating method the pb isotopic data for acid leaching residues are more radiogenic than those for acid washes reflecting efficient removal of non radiogenic pb components by the acid washing among the residues however only those of the agoult and camel donga plagioclase rich fractions yielded isochrons rather than errorchrons with 207pb 206pb ages of 4532 39 0 87 ma and 4515 43 0 42 ma respectively the trace element systematics further suggest that these residues essentially represent contaminant oxide minerals such as ilmenite and chromite rather than plagioclase on the other hand the ar isotopic data for agoult and camel donga yielded plateau ages with weighted means of 4494 9 ma and 3749 25 ma in contrast to those for dag 380 and nwa 049 that did not return any plateau the 207pb 206pb and 40ar 39ar ages of agoult are interpreted to reflect the time of the u pb and k ar system closure during a prolonged thermal metamorphism by combining the ages reported here and in the literature with the calculated closure temperatures the cooling rate of agoult is determined to be 11 2 c ma this cooling rate corresponds to a burial depth of 10 20 km indicating that granulitic eucrites were originally crystallized near the surface and were subsequently buried and metamorphosed the 20 ma younger 207pb 206pb ages of camel donga than agoult are considered to reflect delayed burial metamorphism in the source region whereas the plateau 40ar 39ar age would record the time of an impact causing brecciation and efficient ar degassing of the buried crust furthermore the model 207pb 206pb dates calculated for acid washed pyroxenes imply that the burial metamorphism of agoult and dag 380 were broadly contemporaneous and also that nwa 049 was metasomatized by fluids within the uppermost crust later than 4 4 ga

39ar 40ar ages of eucrites and thermal history of asteroid 4 vesta eucrite meteorites are igneous rocks that derived from a large asteroid probably 4 vesta past studies have shown that after most eucrites formed they underwent metamorphism in temperatures up to 800 c much later many were brecciated and heated by large impacts into the parent body surface the less common basaltic unbrecciated eucrites also formed near the surface but presumably escaped later brecciation while the cumulate eucrites formed at depths where metamorphism may havepersisted for a considerable period to further understand the complex hed parent body thermal history we determined new 39ar 40ar ages for 9 eucrites classified as basaltic but unbrecciated 6 eucrites classified as cumulate and several basaltic brecciated eucrites precise ar ar ages of 2 cumulate eucrites moama and eet 87520 and 4 unbrecciated eucrites give a tight cluster at 4 48 0 02 gyr not including any uncertainties in the flux monitor age ar ar ages of 6 additional unbrecciated eucrites are consistent with this age within theirrelatively larger age uncertainties by contrast available literature data on pb pb isochron ages of 4 cumulate eucrites and 1 unbrecciated eucrite vary over 4 4 4 515 gyr and 147sm 143nd isochron ages of 4 cumulate and 3 unbrecciated eucrites vary over 4 41 4 55 gyr similar ar ar ages for cumulate and unbrecciated eucrites imply that cumulate eucrites do not have a younger formation age than basaltic eucrites as was previously proposed we suggest that these cumulate and unbrecciated eucrites resided at a depth where parent body temperatures were sufficiently high to cause the k ar and some other chronometers to remain as open diffusion systems from the strong clustering of ar ar ages at 4 48 gyr we propose that these meteorites were excavated from depth in a single large impact event 4 48 gyr ago which quickly cooled the samples and started the k ar chronometer a large 460 km crater postulated to exist on vesta may be the source of these eucrites and of many smaller asteroids thought to be spectrally or physically associated with vesta some pb pb and sm nd ages of cumulate and unbrecciated eucrites are consistent with the ar ar age of 4 48 gyr and the few older pb pb and sm nd ages may reflect an isotopic closure before the large cratering event one cumulate eucrite gives an ar ar age of 4 25 gyr 3 additional cumulate eucrites give ar ar ages of 3 4 3 7 gyr and 2 unbrecciated eucrites give ar ar ages of 3 55 gyr we attribute these younger ages to a later impact heating furthermore the ar ar impact reset ages of several brecciated eucrites and eucritic clasts in howardites fall within the range of 3 5 4 1 gyr among these piplia kalan the first eucrite to show evidence for extinct 26al was strongly impact heated 3 5 gyr ago when these data are combined with eucrite ar ar ages in the literature they confirm that several large impact heating events occurred on vesta between 4 1 3 4 gyr ago the onset of major impact heating may have occurred at similar times for both vesta and the moon but impact heating appears to have persisted for a somewhat later time on vesta

postshock annealing and postannealing shock in equilibrated ordinary chondrites implications for the thermal and shock histories of chondritic asteroids abstract in addition to shock effects in olivine plagioclase orthopyroxene and ca pyroxene petrographic shock indicators in equilibrated ordinary chondrites oc include chromite veinlets chromite plagioclase assemblages polycrystalline troilite metallic cu irregularly shaped troilite grains within metallic fe ni rapidly solidified metal sulfide intergrowths martensite and various types of plessite metal sulfide veins large metal and or sulfide nodules silicate melt veins silicate darkening low ca clinopyroxene silicate melt pockets and large regions of silicate melt the presence of some of these indicators in every petrologic type 4 to 6 ordinary chondrite demonstrates that collisional events caused all equilibrated oc to reach shock stages s3 s6 those type 4 to 6 oc that are classified as shock stage s1 on the basis of sharp optical extinction in olivine underwent postshock annealing due to burial beneath materials heated by the impact event those type 4 to 6 oc that are classified s2 on the basis of undulose extinction and lack of planar fractures in olivine were shocked to stage s3 s6 annealed to stage s1 and then shocked again to stage s2 some oc were probably shocked to stage s3 after annealing it seems likely that many oc experienced multiple episodes of shock and annealing because 40ar 39ar chronological data indicate that mil 99301 ll6 s1 was annealed 4 26 ga ago presumably as a consequence of a major impact it seems reasonable to suggest that other equilibrated s1 and s2 oc which contain relict shock features were also annealed by impacts because some type 6 s1 oc e g guarena kernouve portales valley all of which contain relict shock features were annealed 4 44 4 45 ga ago during a period when impacts were prevalent and most oc were thermally metamorphosed it follows that impact induced annealing could have contributed significantly to oc thermal metamorphism

a highly depleted moon or a non magma ocean origin for the lunar crust abstract coupled 146 147 sm 142 143 nd systematics were analyzed on lunar samples that span the range of source compositions created in the early lunar differentiation event ferroan anorthosites high mg suite norite kreep and low and high ti basalts if fit with a single isochron the data agree with previous suggestions of a 250 ma duration for closure of the sm nd system in the lunar interior the two crustal rocks 60025 and 78236 among oldest samples found on the lunar surface have high initial 142 nd 144 nd ratios e 142 nd 0 24 0 27 relative to o chondrites which indicates that they derive from a source strongly depleted in light rare earth elements lree 147 sm 144 nd 0 23 this result suggests either that the moon formed with a strongly superchondritic sm nd ratio or that the lunar crust formed as a product of a post magma ocean remelting of lree depleted cumulates in the lunar interior the basalt data measured here add support to the idea that the lunar interior evolved with a superchondritic sm nd similar to that of the early earth addition of differentiation steps adds complexity and inherit non uniqueness to the interpretation of the lunar nd isotope data but our preferred model has the first stage of lunar evolution 4 567 to 4 44 ga occurring on an already differentiated earth with the moon forming shortly before 4 45 ga and undergoing rapid magma ocean evolution to form the crust the high sm nd source reservoirs of many mare basalt types and kreep by 4 44 ga continued differentiation of the lunar interior through the increasing depletion of the source of high ti mare basalts then continued until 4320 ma

chondrules and matrix in the ornans co3 meteorite possible precursor components abstract bulk compositions of 17 chondrules and one sample of matrix from co3 omans were determined by instrumental neutron activation analysis chondrule precursor components deduced from chondrule compositions are characterized by 1 1 common and slightly volatile siderophiles cr and chalcophiles 2 2 refractory lithophiles and na 3 3 mn si and modal pyroxene and 4 4 feo and olivine component 4 may be closely related to matrix material precursor components have now been inferred for oc eh cv cm and co chondrules a mn and si rich component occurs exclusively among carbonaceous chondrite chondrules although there are significant intergroup differences common to chondrules in all chondrite groups are refractory lithophile rich common siderophile rich and with the exception of eh common lithophile rich components this indicates that the siderophile lithophile and refractory lithophile common lithophile fractionations recorded in chondrite whole rocks were established prior to chondrule formation at all nebular locations

the cooling history of the acapulco meteorite as recorded by the 244pu and 40ar 39ar chronometers 244pu fission track densities recorded in phosphates merrillite and apatite and in orthopyroxenes adjacent to phosphates along with 40ar 39ar dating were used to retrace the cooling evolution in the low temperature regime of the acapulco meteorite over a time interval of 110 ma high resolution 40ar 39ar dating yielded a plateau age of 4514 16 ma and a precise 40ar closure temperature of 560 20 k in plagioclase this ar closure temperature is essentially indistinguishable from the 50 retention temperature of fission tracks registered in orthopyroxene 550 25 k this allows us to anchor the floating relative 244pu timescale to the absolute timescale defined by the 40ar 39ar chronometer plutonium contents of bulk phosphates inferred from fission xenon are 2x higher than those inferred from tracks in the same phosphates reflecting the low track retention temperatures of phosphates however the pu contents from tracks in orthopyroxenes adjacent to phosphates agree with those from fission xenon suggesting similar retention temperatures and times our results together with an estimated peak metamorphic temperature 1300 k and the u pbpb datum of acapulco phosphates gopel et al 1992 outline an early thermochronological history of acapulco that is more detailed than obtained by earlier attempts and spans a time of 160 ma fast cooling in the high temperature regime 1300 720 k of 100 40 k ma was followed by a drastic change of the cooling rate between 720 and 560 k 3 7 k ma down to a very slow cooling 1 7 0 5 k ma from 550 to 360 k the fast cooling at high temperatures shared also by other acapulcoite lodranites a l suggests that the parent body of acapulco was distinctly smaller than the h chondrite asteroid in contrast the very slow cooling in the low temperature regime should imply that acapulco like material became effectively insulated during a later stage of its history 6 ma after the asteroid formation if a formation time of 4565 ma is assumed for the a l body extrapolations back in time of the pu contents of phosphates give initial 244pu 238u ratios of 0 4 10 2 and 11 10 2 for apatite and merrillite respectively for the bulk phosphates an initial pu u value of 0 8 0 16 10 2 is obtained for acapulco which is in full agreement with the preferred chondritic ratio of 0 7 10 2 proposed by hagee et al 1990 trapped ar contents are surprisingly high both primordial 36ar at levels of type 4 ordinary chondrites and excess radiogenic 40ar were detected in our sample as in some acapulcoites by other authors this partial closed system behaviour could be the result of the partial melt and sintering effects that the high peak metamorphic temperatures have induced in a l meteorites in addition the spread in the early peak temperatures 1300 1450 k as reflected by the diverse degrees of partial melting observed in a l meteorites suggests heterogeneously distributed short lived heating sources 26al60fe and disfavours the homogeneous heating expected from an electromagnetic induction arising from an active pre main sequence sun the possibility that some specific collisional event s with or without disruption of the a l planetesimal could satisfactorily explain the thermal histories and diverse characteristics of these meteorites appears difficult to envision in the absence of evident shock effects in most if not all a l meteorites

metal and associated phases in bishunpur a highly unequilibrated ordinary chondrite it appears that the highly unequilibrated bishunpur ordinary chondrite preserves phase relations acquired during solar nebular processes to a relatively high degree metamorphic temperatures may not have exceeded 300 350 c the major categories of metal are 3 kinds of metal in the metal matrix three kinds in chondrule interiors and 2 kinds in chondrule rims the fine grained matrix metal is highly variable in composition the kamacite co content 7 8 2 0 mg g is within the l group range 6 7 8 2 mg g but extends well above and below its ni content 38 5 mg g is considerably lower than in more equilibrated chondrites and taenite is ni rich 450 mg g and unzoned these compositions imply equilibration at very low temperatures of about 300 350 c it seems unlikely that volume diffusion could account for the observed relatively unzoned phases a better model involves mass transport by grain boundary diffusion and grain growth at the indicated temperatures we find no evidence that the matrix was ever at higher temperatures large 50 650 m polycrystalline metal aggregates consisting of individually zoned crystals are also found in the matrix they probably represent clusters formed in the solar nebula a few large 50 250 m round monocrystalline grains are also present in the matrix metal bearing chondrules tend to be highly reduced they contain low ni metal that occasionally contains si and or cr silicates in these chondrules tend to have low feo feo mgo ratios the si rich metal grains are never in contact with silicates and are always surrounded by troilite with a poorly characterized ca cr sulfide at the metal troilite interface they appear to be high temperature nebular condensates that avoided oxidation even during the chondrule forming process silicon contents drop below our detection limit when the sulfide coating is absent much more common in chondrule interiors are si free spheroidal metal grains not associated with sulfides these have ni and co contents very similar to the si bearing grains and appear to be oxidized variants of the same material the third class of chondrule metal is fine 1 m dusty grains inside individual olivine grains these seem to reflect high temperature in situ reduction of feo from the olivine the composition of kamacite is different in sulfide rich and sulfide poor chondrule rims and in both cases it is dissimilar to the compositions in the chondrule interiors and matrix this indicates that chondrule rims could not have resulted from reactions with the matrix but are primary features acquired prior to accretton

manganese chromium formation intervals for chondrules from the bishunpur and chainpur meteorites whole chondrule mn cr isochrons are presented for chondrules separated from the chainpur ll3 4 and bishunpur ll3 1 meteorites the chondrules were initially surveyed by instrumental neutron activation analysis ll chondrite normalized mn cr mn fe and sc fe served to identify chondrules with unusually high or low mn cr ratios and to correlate the abundances of other elements to sc the most refractory element measured a subset of chondrules from each chondrite was chosen for analysis by a scanning electron microscope equipped with an energy dispersive x ray spectrometer prior to high precision cr isotopic analyses 53cr 52cr correlates with 55mn 52cr to give initial 53mn 55mn i 9 4 1 7 10 6 for chainpur chondrules and 53mn 55mn i 9 5 3 1 10 6 for bishunpur chondrules the corresponding chondrule formation intervals are respectively tlew 10 1 ma for chainpur and 10 2 ma for bishunpur relative to the time of igneous crystallization of the lewis cliff lew 86010 angrite because mn sc correlates positively with mn cr for both the chainpur and bishunpur chondrules indicating dependence of the mn cr ratio on the relative volatility of the elements we identify the event dated by the isochrons as volatility driven elemental fractionation for chondrule precursors in the solar nebula thus our data suggest that the precursors to ll chondrules condensed from the nebula 5 8 2 7 ma after the time when initial 53mn 55mn i 2 8 0 3 10 5 for calcium aluminum rich inclusions cais our preferred value determined from data for a mineral separates of type b allende cai br1 b spinels from efremovka cai e38 and c bulk chondrites mn cr formation intervals for meteorites are presented relative to average i mn 53mn 55mn ch 9 46 10 6 for chondrules mn cr ratios for radiogenic growth of 53cr in the solar nebula and later reservoirs are calculated relative to average i mn 53cr i 9 46 0 08 10 6 0 23 0 08 for chondrules inferred values of mn cr lie within expected ranges thus it appears that evolution of the cr isotopic composition can be traced from condensation of cais via condensation of the ferromagnesian precursors of chondrules to basalt generation on differentiated asteroids measured values of 53cr for individual chondrules exhibit the entire range of values that has been observed as initial 53cr values for samples from various planetary objects and which has been attributed to radial heterogeneity in initial 53mn 55mn in the early solar system estimated 55mn 52cr 0 42 0 05 for the bulk earth combined with 53cr 0 for the earth plots very close to the chondrule isochrons so that the earth appears to have the mn cr systematics of a refractory chondrule thus the earth apparently formed from material that had been depleted in mn relative to cr contemporaneously with condensation of chondrule precursors if as seems likely the earth s core formed after complete decay of 53mn there must have been little differential partitioning of mn and cr at that time

old sm nd ages for cumulate eucrites and redetermination of the solar system initial 146sm 144sm ratio article i nfo sm 142 nd systematics short lived 146 sm 142 nd and long lived 147 sm 143 nd chronometers have been measured in three cumulate eucrites binda moore county and moama the two major mineral phases plagioclase and pyroxene present in these achondrites are characterized by a wide range of sm nd ratios that allows well resolved sm nd isochrons this group of meteorites thus is suitable to better constrain the initial 146 sm 144 sm ratio of the solar system binda and moore county give concordant ages of 4544 88 and 4542 85 ma respectively with initial 143 nd 144 nd ratios slightly higher to within error of chondritic these ages are in agreement with most of the radiometric ages determined on basaltic eucrites a best estimate for the solar system initial 146 sm 144 sm ratio is obtained using the five point regression line determined for binda the 146 sm 144

k mg ti and ca isotopic compositions and refractory trace element abundances in hibonites from cm and cv meteorites implications for early solar system processes potassium and magnesium isotopic compositions of hibonites from the murchison cm and allende cv meteorites are determined by an ion microprobe to look for possible presence of the short lived nuclides 41ca and 26al at the time of their formation abundance anomalies in the neutron rich isotopes 50ti and 48ca as well as ree and additional refractory trace element abundances have also been determined to infer a plausible formation environment of the hibonites in the early solar system the results obtained in this study suggest a widespread distribution of the short lived nuclide 41ca in the early solar system observation of correlated presence of the two short lived nuclides 41ca and 26al on a microscopic scale in refractory hibonites and silicates from cm and cv meteorites suggests these nuclides to be cogenetic and support a stellar source for these and several other short lived nuclides in the early solar system moderate to high enrichments in the neutron rich isotopes 50ti and 48ca are seen in some of the analyzed hibonites our data for radiogenic and stable isotopic anomalies as well as refractory trace element abundance patterns in isolated cm hibonites with platelet morphology show trends similar to those reported earlier they are devoid of 41ca and 26al show large enrichment in 50ti and 48ca and have typical group iii ree patterns however hibonites present within hibonite spinel inclusions show variations in their ree patterns one of them shows the normally expected group ii ree pattern while another has an ultrarefractory ree pattern and a third has affinities towards platelet hibonites that appear to suggest a link between these two groups of hibonites with distinct morphological characteristics we propose a new model to explain the absence of the short lived nuclides 41ca and 26al in some of the hibonites whose ree abundance patterns and stable isotopic anomalies suggest that they are some of the first solar system solids assuming a stellar origin for these nuclides we attribute this absence to the very early formation of these hibonites near the central region of the collapsing protosolar cloud prior to the arrival of the short lived nuclides injected into the cloud from a stellar source

aluminum 26 in calcium aluminum rich inclusions and chondrules from unequilibrated ordinary chondrites in order to investigate the distribution of 26 a1 in chondrites we measured aluminum magnesium systematics in four calcium aluminum rich inclusions cais and eleven aluminum rich chondrules from unequilibrated ordinary chondrites uocs all four cais were found to contain radiogenic 26 mg 26 mg from the decay of 26 a1 the inferred initial 26 al 27 al ratios for these objects 26 al 27 al 0 5 10 5 are indistinguishable from the 26 al 27 al 0 ratios found in most cais from carbonaceous chondrites these observations together with the similarities in mineralogy and oxygen isotopic compositions of the two sets of cais imply that cais in uocs and carbonaceous chondrites formed by similar processes from similar or the same isotopic reservoirs or perhaps in a single location in the solar system we also found 26 mg in two of eleven aluminum rich chondrules the 26 al 27 al 0 ratio inferred for both of these chondrules is 1 10 5 clearly distinct from most cais but consistent with the values found in chondrules from type 3 0 3 1 uocs and for aluminum rich chondrules from lightly metamorphosed carbonaceous chondrites 0 5 10 5 to 2 10 5 the consistency of the 26 al 27 al 0 ratios for cais and chondrules in primitive chondrites independent of meteorite class implies broad scale nebular homogeneity with respect to 26 al and indicates that the differences in initial ratios can be interpreted in terms of formation time a timeline based on 26 al indicates that chondrules began to form 1 to 2 ma after most cais formed that accretion of meteorite parent bodies was essentially complete by 4 ma after cais and that metamorphism was essentially over in type 4 chondrite parent bodies by 5 to 6 ma after cais formed type 6 chondrites apparently did not cool until more than 7 ma after cais formed this timeline is consistent with 26 al as a principal heat source for melting and metamorphism

ni isotopic compositions in allende and other meteorites abstract a new technique for high precision isotopic analyses of ni was developed and applied to terrestrial samples allende inclusions and materials from other meteorites most of the allende inclusions analysed here were previously reported to contain isotopically anomalous ti in contrast the ni isotopic abundances are indistinguishable from normal within presently obtainable precision with only one possible exception the latter inclusion was shown by others to contain a significantly fractionated magnesium isotopic pattern of 9 amu a normal ni isotopic pattern has also been observed for the chromite carbon fraction of an allende acid residue which is known to contain heavy noble gases of highly anomalous isotopic composition all other meteoritic samples analysed khohar matrix and chondrules murray matrix a tieschitz chondrule and an orgueil magnetic fraction also show normal isotopic compositions of ni no evidence for effects from now extinct60fe could be detected in spite of ubiquitous isotopic anomalies in ti from normal allende inclusions there is no signature of isotopic variations in ni from the same samples possible constraints for the nucleosynthesis of iron peak elements and for astrophysical and cosmochemical conditions during formation of the solar system are discussed

stability analyses of rainfall induced landslides the slope stability issues concerning rainfall induced slope failures are investigated and presented specifically the effect of both negative and positive pore water pressures on the stability of initially unsaturated slopes are carefully explained and coupled with infinite slope analysis methods in order to present a predictive formulation of slope failures that occur as a result of rainfall events the formulation serves as a baseline analysis method for evaluating potentially unstable soil slopes that are subject to surface infiltration and explains the various triggering mechanisms that may occur based on individual combinations of the slope geometry soil strength and infiltration parameters a procedural method is outlined for utilizing the analytical formulation to predict the change in the factor of safety for a slope subject to infiltration and a detailed analysis of a case study is presented to verify the method quantitative statements are made concerning the time and depth of failure in relationship to the soil slope and rainfall parameters

mega chondrules and large igneous textured clasts in julesberg l3 and other ordinary chondrites vapor fractionation shock melting and chondrule formation abstract a petrographic microprobe study of large metal poor igneous textured objects in julesberg l3 and other ordinary chondrites suggests that they can be classified into two petrographic types mega chondrules and large lithic clasts and into two chemical types na poor and na rich mega chondrules show textural evidence of having solidified as freely floating melt droplets whereas lithic clasts formed by the fragmentation of larger objects possibly still larger mega chondrules barred olivine or barred olivine pyroxene textures are most common for mega chondrules whereas a variety of textures occur in large lithic clasts the two petrographic types cannot be distinguished on the basis of modal bulk or phase compositions sodium poor objects are characterized by 1 plagioclase or glass with mainly bytownite composition an70 90 typical 2 subchondritic na al ratios and typically subchondritic volatile element na k and mn abundances and 3 bulk chemical trends that resemble those expected for vapor fractionation processes some na poor objects may have formed by the melting of precursors that formed as condensates or vaporization residues others may have formed by the melting of precursors that formed by fractional condensation or fractional vaporization following vapor fractionation na poor objects or their precursors appear to have reequilibrated at lower temperatures which raised the bulk na content of the objects but not to the levels seen in na rich objects enrichments of fe2 na k and p on the margins of some na poor objects suggest that they partly reacted with volatile rich surroundings both before and after brecciation sodium rich objects are characterized by 1 plagioclase or glass with oligoclase or albite composition an2 25 2 roughly chondritic na al ratios and volatile element na k mn abundances and 3 bulk chemical trends similar to those shown by melt pocket glasses in ordinary chondrites sodium rich melt objects could have formed by the shock melting of chondritic precursors feldspathic compositions for some na rich melt objects can be explained by preferential shock melting of feldspar or feldspathic glass in chondritic target materials literature data imply that the same two chemical populations of objects na poor and na rich occur among smaller normal sized chondrules in type 3 ordinary chondrites suggesting that the same processes that affected large melt objects also affected chondrules

u pb and 207pb 206pb ages of zircons from basaltic eucrites implications for early basaltic volcanism on the eucrite parent body we have undertaken petrologic and shrimp u th pb isotopic studies on zircons from basaltic eucrites yamato y 75011 y 792510 asuka a 881388 a 881467 and padvarninkai with different thermal and shock histories eucritic zircons are associated with ilmenite in most cases and have subhedral shapes in unmetamorphosed and metamorphosed eucrites some zircons in highly metamorphosed eucrites with granulitic texture occur alone in pyroxene and typically have rounded to subrounded shapes due to recrystallization superchondritic zr hf ratios of eucritic zircons indicate that they crystallized from incompatible element rich melts after crystallization of ilmenite concentrations of uranium and thorium in zircons in the unmetamorphosed eucrite y 75011 are higher than those in metamorphosed eucrites the u pb systems of eucritic zircons are almost concordant but some zircon grains show reverse discordance radiogenic lead loss up to 48 from zircons is observed in the shock melted eucrite padvarninkai the 207pb 206pb ages of zircon in y 75011 4550 9 ma n 5 are nearly identical within analytical uncertainty to the ages of zircons from the metamorphosed eucrite y 792510 4545 15 ma n 13 the highly metamorphosed eucrites a 881388 4555 54 ma n 5 and a 881467 4558 13 ma n 8 and the shock melted eucrite padvarninkai 4555 13 ma n 18 the averaged 207pb 206pb age of zircon from five eucrites analyzed in this study is 4554 7 ma 95 confidence limits n 49 indistinguishable from the averaged u pb age 4552 9 ma of the same samples because of the high closure temperature of lead in zircon tclosure 1050 c with a cooling rate of 0 2 c yr the 207pb 206pb ages of eucritic zircon do not represent metamorphic ages but crystallization ages of extrusive lavas this fact strongly suggests that volcanism of the eucrite parent body occurred at a very early stage of the solar system history 7 20 ma after cai formation 4567 2 0 6 ma thus basaltic eucrites crystallized from parental magmas within a short interval following the differentiation of their parent body the u pb ages of eucritic zircons are older than the u pb sm nd and rb sr ages of some basaltic eucrites which is consistent with differences in closure temperatures of each isotopic system and suggests that thermal and shock metamorphism affected the isotopic systems of pyroxene plagioclase and phosphates

shock and thermal history of northwest africa 4859 an annealed impact melt breccia of ll chondrite parentage containing unusual igneous features and pentlandite abstract northwest africa 4859 nwa 4859 is a meteorite of ll chondrite parentage that shows unusual igneous features and contains widely distributed pentlandite the most obvious unusual feature is a high proportion of large 3 cm diameter igneous textured enclaves lites interpreted as shock melts that were intruded into an ll chondrite host one such lite appears to have been produced by whole rock melting of ll chondrite initial rapid partial crystallization and subsequent slow cooling of the residual melt in the host to produce a differentiated object other unusual features include mm sized overgrowth objects fine grained plagioclase rich bands and coarse troilite 7 mm across grains all these features are interpreted as having crystallized from melts produced by a single transient shock event followed by slow cooling a subsequent shock event of moderate s3 intensity produced veining and transformed some of the pyroxene into the clinoenstatite polytype pentlandite together with associated troilite in nwa 4859 probably formed by the breakdown of a monosulfide precursor phase at low temperature 230 c following the second shock event nwa 4859 is interpreted to be an unusual impact melt breccia that contains shock melt which crystallized in different forms at depth within the parent body

60fe in eucrites additional evidence for the existence in the early solar system of live60fe has been found in the basaltic achondrite juvinas the relative abundance of 60fe 56fe of x0223c 4 10 10 at the time of meteorite solidification is one order of magnitude lower than that previously observed for the eucrite chervony kut this difference corresponds to a 4 7 ma time interval between closure of the60fe 60ni isotopic system in the two meteorites the factor two higher initial 60ni 58ni ratio in juvinas is consistent with this time difference and a common bulk fe ni ratio in the two meteorites using the60fe 60ni isotope system as a chronometer various models for the evolution of the eucrite parent body of different degrees of complexity are discussed regardless of the detailed differences between these models a short time interval of only a few million years between planetary differentiation and basaltic crust formation is indicated

hf w internal isochrons for ordinary chondrites and the initial 182hf 180hf of the solar system abstract three ordinary chondrites forest vale h4 ste marguerite h4 and richardton h5 have been studied with 182 hf 182 w system t1 2 9 million years m y in order to provide constraints on the initial 182 hf 180 hf for the chondritic parent body and the solar system all three samples display positive correlations between 182 w 184 w and 180 hf 184 w providing confirmation that live 182 hf was present in these samples the best fit lines define comparable slopes passing through or close to the data for the bulk carbonaceous chondrites allende and murchison at the current level of resolution this indicates a common and well mixed chondritic reservoir in terms of the hf w isotope system forest vale yields the most precise results with an apparent initial 182 hf 180 hf of 1 87 0 16 10 4 and an initial 182 w 184 w of 0 864710 15 if the pb pb phosphate age of forest vale 5 m y younger than the pb pb age of allende cai is a formation age the bulk solar system initial 182 hf 180 hf is estimated to be 2 75 0 24 10 4 comparable to previous estimates based on the differences in w isotopic compositions between iron meteorites and the mean of carbonaceous chondrites the solar system 182 w 184 w initial of 0 86457 4 ew 4 99 0 46 is similar to the least radiogenic w reported for iron meteorites suggesting an extremely early origin of their parent bodies and the segregation of metallic cores from planetesimals the solar system 182 hf 180 hf initial obtained in this study is high relative to the initial abundances of other short lived nuclides including those with longer half lives such as 129 i t1 2 16 m y however this result is explicable with the model of wasserburg et al wasserburg g j busso m gallino r 1996 abundances of actinides and short lived nonactinides in the interstellar medium diverse supernova sources for the r processes astrophys j 466 l109 113 who have proposed that 182 hf is synthesized in the same r process supernovae events that produced the actinides over most of galactic history

the origin of eucrites diogenites and olivine diogenites magma ocean crystallization and shallow magma chamber processes on vesta the asteroid 4 vesta is one of the very few heavenly bodies to have been linked to samples on earth the howardite eucrite diogenite hed meteorite suite this large and diverse suite of meteorites provides a detailed picture of vesta s igneous and postigneous history we have used the range of igneous rock types and compositions in the hed suite to test a series of chemical models for solidification processes following peak melting magma ocean conditions on vesta fractional crystallization cannot have been a dominant early process in the magma ocean because it leads to excessive fe enrichment in the melt models that are dominated by equilibrium crystallization cannot produce orthopyroxene cumulates diogenites our best models invoke 60 70 equilibrium crystallization of a magma ocean followed by continuous extraction of the residual melt into shallow magma chambers fractional crystallization in these magma chambers combined with continuous or periodic addition of more melt from the slowly compacting crystal mush magmatic recharge can produce all of the igneous hed lithologies noncumulate and cumulate eucrites diogenites dunites harzburgites and olivine diogenites magmatic recharge can also explain the narrow range in eucrite compositions and the variability of incompatible trace element concentrations in diogenites we predict an internal structure for vesta that permits excavation of the heds during the formation of the rheasilvia basin while remaining consistent with observations from the dawn mission and most impact models

sodium chlorine rich mesostases in chainpur ll3 and parnallee ll3 chondrules forty six chondrules from chainpur ll3 4 and 39 chondrules and clasts from parnallee ll3 6 have been sectioned and searched for na cl rich phases by electron probe microanalysis epma oxygen isotopic compositions i xe ages and ion probe data were also obtained on some of these chondrules sodium cl rich glass and microcrystalline sodalite na4al3si3o12cl nepheline naalsio4 scapolite na4al3si9o24cl have been identified in 7 of the chainpur and 8 of the parnallee samples these phases are present in chondrule mesostases or in one case the plagioclase of a barred olivine chondrule none of the chondrules contain 5 vol na cl rich phases in the chainpur chondrules they originated through partial devitrification of silica undersaturated rare earth element ree na and cl rich mesostases two processes have been identified that led to the formation of these mesostases in two of the chondrules which consist mainly of low ca pyroxene the extended metastable crystallization of low ca pyroxene created silica undersaturated ree rich residua barium and cl enrichments in nepheline and scapolite of one chondrule suggest that there was also an influx of alkalis and cl during crystallization of the low ca pyroxene similarly another one of the chainpur chondrules mainly composed of olivine phenocrysts is markedly enriched in cl 10 oc as there is no evidence of corrosive metasomatism in any of the chondrules cl and alkali enrichment is believed to have occurred when they were still partially molten the chondrules were derived from normal o isotopic reservoirs so the postulated influx of ba na and cl did not occur on an exotic parent body trace amounts of nepheline and sodalite present in two parnallee chondrules crystallized from small na cl ree rich residua following extended crystallization of anorthite an i xe age of 5 0 ma post bjurbole obtained on one of these parnallee chondrules dates the crystallization of feldspathoid and thus formation of the chondrule

comparative study of equilibrated and unequilibrated eucrites subsolidus thermal histories of haraiya and pasamonte thermal histories of non cumulate eucrites pasamonte and haraiya were determined from ca ca fe mg profiles of host lamellae pyroxene pairs from compositional profiles of pyroxene rims affected by metasomatism and from lamellae thicknesses using a rate law for lamellar coarsening pasamonte a type 2 eucrite experienced partial equilibration during a relatively short period of thermal annealing this equilibration is expressed texturally by metasomatized rims in mg rich and fe rich pyroxene grains and by coarsening of nanometer scale exsolution lamellae a cooling rate of 10 2 c day corresponds to post impact mixing and reburial of the polymict pasamonte assemblage to a depth similar to that of the initial lava flow haraiya a type 7 eucrite has experienced a complex thermal history involving multiple brecciation events and mixing of a single flow to produce a monomict assemblage containing clasts of variable grain size and texture a period of thermal annealing 50000 years in duration at temperatures between 1000 and 700 c corresponding to a cooling rate of 10 4 to 10 5 c day produced augite exsolution up to 3 m thick in pigeonite rapid burial by successive flows during a period of high magma productivity and high heat flow due to 2 6 al decay in the crust and mantle was a possible source of heat for metamorphism in the lower crust however cooling rates during relaxation of the lower crustal thermal gradient are much less than the mineralogically determined cooling rates heat derived from impact or from mid to upper crustal level intrusions is a plausible heat source for metamorphism and is consistent with observed cooling rates

zoned chondrules in semarkona evidence for high and low temperature processing at least 15 of the 10w feo chondrules in semarkona ll3 0 have mesostases that are concentrically zoned in na with enrichments near the outer margins we have studied zoned chondrules using electron microprobe methods x ray mapping plus quantitative analysis ion microprobe analysis for trace elements and hydrogen isotopes cathodoluminescence imaging and transmission electron microscopy in order to determine what these objects can tell us about the environment in which chondrules formed and evolved mesostases in these chondrules are strongly zoned in all moderately volatile elements and h interpreted as water calcium is depleted in areas ofvolatile enrichment titanium and cr generally decrease toward the chondrule surfaces whereas al and si may either increase or decrease generally in opposite directions to one another mn follows na in some chondru1es but not in others fe and mg are unzoned d h ratios increase in the water rich areas of zoned chondrules mesostasis shows cathodoluminescence zoning in most zoned chondrules with the brightest yellow color near the outside mesostasis in zoned chondrules appears to be glassy with no evidence for devitrification systematic variations in zoning patterns among pyroxene and olivine rich chondrules may indicate that fractionation oflow and high ca pyroxene played some role in ti cr mn si ai and some ca zoning but direct condensation ofelements into hot chondrules secondary melting oflate condensates into the outer portions of chondrules and subsolidus diffusion of elements into warm chondrules cannot account for the sub parallel zoning profiles ofmany elements the presence ofh20 or elemental abundance patterns zoning ofmoderately volatile elements and ca may have been produced by hydration ofchondrule glass without devitrification during aqueous alteration on the parent asteroid this could have induced structural changes in the glass allowing rapid diffusion and exchange of elements between altered glass and surrounding matrix and rim material calcium was mainly lost during this process and other nonvolatile elements may have been mobile as well some unzoned 10w feo chondrules appear to have fully altered mesostasis

in situ 60fe 60ni systematics of chondrules from unequilibrated ordinary chondrites abstract the initial 60fe 56fe of chondrules from unequilibrated ordinary chondrites uocs can potentially constrain the stellar source of short lived radionuclides and develop the 60fe 60ni t1 2 2 6 ma system for early solar system chronology however progress with the 60fe 60ni system has been hindered by discrepancies between initial ratios inferred from bulk and in situ fe ni analyses telus et al 2016 show that discrepancies between these different techniques stem from late stage open system fe ni mobilization here we report in situ analyses of the fe ni isotopic composition of ferromagnesian silicates in chondrules from uocs using the ion microprobe of the 24 chondrules analyzed for this study a few chondrules have resolved excesses in 60ni of up to 70 however the correlations with fe ni are weak although complications from fe ni redistribution make it difficult to interpret the data we show that the initial 60fe 56fe for uoc chondrules is between 5 10 8 and 3 0 10 7 this is consistent with a late supernova source for 60fe but self enrichment of the molecular cloud is another possible mechanism for incorporating 60fe in the solar system discrepancies between bulk and in situ analyses remain but likely stem from late stage open system fe ni mobilization

147sm 143nd and 176lu 176hf in eucrites and the differentiation of the hed parent body the 147sm 143nd and 176lu 176hf systematics of 21 whole rock eucrites including five cumulates have been investigated by mc icp ms a statistically significant sm nd isochron was obtained on 18 samples with an age of 4464 75 ma mswd 1 26 and an intercept of 0 50680 0 00010 this age clearly is controlled by the cumulate eucrites the 21 basaltic and cumulate eucrites together do not form a statistically significant lu hf isochron basaltic eucrites however form an errorchron with an age of 4604 39 ma mswd 4 52 which becomes an acceptable isochron if the error on the lu hf ratio is doubled with respect to the laboratory estimate the initial 176hf 177hf is 0 27966 0 00002 three of the cumulate eucrites regressed together further yield a statistically significant age of 4470 22 ma indistinguishable from their sm nd age we therefore conclude that cumulate eucrites are 100 myr younger than basaltic eucrites and basaltic eucrites are close in age to the solar system there is no evidence in the present data to support a decay constant of 176lu significantly different from 1 93 10 11 yr 1 sguigna can j phys 60 1982 361 364 the broad range of variation and strong correlation of lu hf and sm nd ratios require that eucrites are partial melts and not residual magmas the relative lu hf and sm nd fractionation is controlled by the plagioclase to mafic mineral ratio in the residue the steep correlation between these two ratios is explained by the enhancement of plagioclase saturation in the low gravity field of the eucrite parent body basaltic eucrites probably formed as large degree melts of a chondritic source the strong lu hf and sm hf fractionation observed in cumulates clearly reflects the presence of residual ilmenite during melting our preferred interpretation is that cumulates were impregnated by small degree melts of ilmenite bearing gabbros since pressure on the eucrite parent body never reaches the garnet stability field this observation questions the ubiquitous presence of residual garnet in the mantle sources of magmas formed on larger planets such as the moon mars and possibly earth

upb systematics of phosphates from equilibrated ordinary chondrites u pb systematics were determined from fifteen phosphate separates from equilibrated ordinary chondrites and from small bulk fragments of the same meteorites the high 238u204pb ratios of thirteen of these phosphate separates lead to extremely radiogenic pb whose 206pb204pb ratios range from 250 up to 3500 the pb pb model ages for these phosphates range from 4 563 to 4 502 ga with an analytical precision of 106 y and the u pb system is apparently concordant the time interval observed 60 106 y reflects the thermal processing of the equilibrated chondrites and is consistent with that previously derived from the rb sr k ar and pu chronologies the pb pb ages of the phosphates from the seven h chondrites show a negative correlation versus their metamorphic grade this is the first clear relationship ever observed between a long lived chronometer and the intensity of metamorphism as reflected by metamorphic grade assuming that the pb pb age indicates the accurate u pb closure time in phosphates the pb pb chronology is compatible with the model of a layered h chondrite parent body however this interpretation of the u pb systematics is not unique it postulates a slow cooling of the equilibrated materials at high temperature in apparent conflict with petrological observations except for the h chondrites which agree rather well with pu systematics comparison of the pb pb chronology with published radiochronometric data does not reveal simple correlations in the present debate concerning the thermal history of chondrites the chronometric information derived from each isotope system is interpreted as the time of its thermal closure however this basic assumption may not be correct for all the radiochronologies and must be evaluated before the radiochronometric data can be applied as compelling time constraints for the period of 4 56 4 4 ga of proto planetary history

evidence for primitive nebular components in chondrules from the chainpur chondrite abstract the least equilibrated ordinary chrondrites contain chondrules which have experienced little change since the time of their formation in the early solar system these chondrules are excellent indicators of the physical and chemical nature of the solar nebula we separated 36 chondrules from the chainpur ll3 4 chondrite and analyzed each for 20 elements and petrographic properties sampling biases were minimized as far as possible chondrules seem to have formed through the melting of random mixtures of grains comprising a limited number of nebular components the identity of these components can be deduced from chondrule compositions the dominant components appear to be 1 a mixture of metal and sulfide with composition similar to whole rock metal and sulfide 2 refractory ir rich metal 3 refractory olivine rich silicates 4 low temperature pyroxene rich silicates and possibly 5 a component containing the more volatile lithophiles most of the textural types of chondrules formed from the same set of precursor components in some cases chondrules having different textures are almost identical in composition a few unusual chondrule types seem to mainly consist of uncommon nebular components possibly indicating different modes of formation etching experiments confirm that chondrule rims are enriched in metal troilite and moderately volatile elements relative to the bulk chondrules however a large fraction of the volatiles remains in the unetched interior

thermoluminescence sensitivity and thermal history of type 3 ordinary chondrites eleven new type 3 0 3 1 chondrites and possible explanations for differences among h l and ll chondrites we review induced thermoluminescence tl data for 102 unequilibrated ordinary chondrites uocs many data just published in abstracts in order to identify particularly primitive uocs and further explore tl systematics that may have implications for the history of the chondrites and their parent body we have identified 11 uocs of petrologic types 3 0 3 1 adrar 003 elephant moraine eet 90066 eet 90161 grosvenor mountains gro 95502 lewis cliff lew 88477 meteorite hills met 96503 yamato y 790787 y 791324 y 791558 y 793565 and y 793596 these samples represent an important new resource for researchers interested in the nature of primitive solar system materials previously reported trends in which tl sensitivity increases with tl peak temperature and tl peak width which we interpret in terms of crystallization of feldspar in the ordered or disordered forms during metamorphism are confirmed by the new data importantly the present data strengthen the trend described earlier in which the mean level of metamorphism experienced by uocs increases along the series ll l and h this suggests either different burial depths for the uocs from each class or formation at similar depths in regoliths of different thickness

petrology and mineralogy of type ii feo rich chondrules in semarkona ll3 0 origin by closed system fractional crystallization with evidence for supercooling abstract the petrology of type ii porphyritic olivine chondrules in semarkona ll3 0 has been studied in detail olivines in these chondrules are euhedral fe richand are strongly zoned from cores to rims of grains in feo fa10 30 cr2o3 0 2 0 6 wt mno 0 2 0 7 wt and cao 0 1 0 4 wt interstitial mesostasis is rich in si aland ca and is glassy with abundant microcrystallites minor minerals include troilite fe ni metaland chromite some olivine grains contain euhedral fayalite rich cores that are probably produced during initial supercooling of the chondrule melt rare relict grains of forsteritic olivine have compositions very similar to olivines in type ia chondrules in semarkona and may result from disaggregation of such chondrules apart from these relics all properties of type ii chondrules can be described by closed system fractional crystallization of droplets which were essentially entirely molten the chondrules did not originate as aggregates of large olivine grains and are unlikely to be fragments of precursor igneous rocks cooling rates of the order of 1000 c h are indicated from peak temperatures of around 1600 c the chondrules show considerable evidence for supercooling and large departures from equilibrium during crystallization there is no evidence for chondrule nebula exchange either during or after crystallization or any secondary processes such as aqueous alteration or thermal metamorphism bulk composition data suggest that precursor material included a refractory ca al ti rich component similar to one of the precursor components of type ia chondrulesand a non refractory fe and si rich component type ia chondrules may have formed from type ii chondrules by loss of fe and volatiles alternatively the two chondrule types may have formed in regions of considerable diversity in the solar nebula from precursor materials with different fe mg ratios

retention of sodium during chondrule melting abstract type i chondrules in unequilibrated ordinary and carbonaceous chondrites tend to be enriched in refractory elements and depleted in volatiles relative to bulk ci type ii chondrules show chondritic concentrations of major and minor lithophile elements with na in particular at or slightly above the appropriate bulk rock values element ratio diagrams for chondrule bulk compositions show that type ii chondrules plot on a mixing line between forsterite and a na phase with na al 1 1 whereas type i compositions can be explained by mixing forsterite with melilite or cai or other refractory component with little na calcium in type ii chondrules must have been added as an al free phase such as diopside if their bulk compositions are manipulated subtracting ca as diopside and fe mg as olivine the residue is 90 albite and 10 silica which would be in pyroxene albite was incorporated into the precursors of type ii chondrules which clearly have not been depleted in na although their initial temperatures overlap with those of type i there is no negative correlation between type i liquidus temperatures 1450 1900 c and na al ratios and hence no indication of na loss from the melt if type i precursors contained albite the most aluminous chondrules would have suffered the most extreme na loss but these have the lowest liquidus temperatures their precursors were na depleted whereas those of type ii were na enriched as a function of the abundance of albite the simplest way to obtain the bulk compositions of chondrules is to assemble condensates into precursors at different temperatures and concentration of solids in the nebula or exceptionally rapid heating is required to preserve na in chondrules after melting substantial exchange of na occurred between chondrules and chondrite matrix during parent body metamorphism to petrologic type 3 6

on early solar system chronology implications of an heterogeneous spatial distribution of 26al and 53mn abstract early solar system chronology is usually built with the assumption that the distribution of short lived radionuclides was homogeneous through the solar accretion disk at present there is no unambiguous evidence for a homogeneous distribution of short lived radionuclides in the solar accretion disk while some data point to a heterogeneous distribution of short lived radionuclides in this paper we explore a possible chronology based on a heterogeneous distribution of 26 al and 53 mn in the accretion disk our basic assumption is that the different abundances of extinct short lived radionuclides in calcium aluminium rich inclusions cais and chondrules are due to spatial rather than temporal differences we develop a simple model where cais and chondrules form contemporaneously in different spatial locations and are characterised by distinct initial 26 al and 53 mn abundances in this model all evolved bodies are supposed to be originally chondritic i e to be made of a mixture of cais chondrules and matrix this mixture determines the initial content in 26 al and 53 mn of a chondritic parent body as a function of its cai and chondrule abundance fraction this approach enables us to calculate coherent 26 al and 53 mn ages from the agglomeration of the parent body precursors cais and chondrules until the isotopic closure of 26 al and 53 mn thereafter called 26 al 53 mn age we calculate such 26 al 53 mn ages for a diversity of evolved objects with the constraint that they should be found for realistic chondritic parent body precursors i e objects having similar or identical petrograpy to the existing chondrite groups the so defined age of the d orbigny angrite is 4 3 1 1 myr for the asuka 881394 eucrite 2 8 1 0 myr for the h4 chondrite sainte marguerite 3 myr and for h4 forest vale 5 myr the calculated 26 al 53 mn ages give timescales for the evolution of the respective parent bodies meteorites that can be investigated in the light of further petrographic studies we anchor the calculated relative chronology to an absolute chronology using absolute pb pb ages and relative hf w ages of the objects under scrutiny the precursors of sainte marguerite and forest vale agglomerated at the same time 4565 8 1 2 ma ago the precursors of eucrites asuka 881394 agglomerated 4564 8 1 2 ma ago the precursors of angrites agglomerated late 4561 5 1 8 ma ago our model provides a fully compatible al mg mn cr pb pb chronology and is shown to be robust to reasonable changes in the input parameters the calculated initial 26 al 27 al ratios are high enough to have 26 al as a possible heat source for differentiation

reconciliation of the excess 176 hf conundrum in meteorites recent disturbances of the lu hf and sm nd isotope systematics abstract the long lived 176 lu 176 hf and 147 sm 143 nd radioisotope systems are commonly used chronometers but when applied to meteorites they can reveal disturbances specifically lu hf isochrons commonly yield dates up to 300 myr older than the solar system and varying initial 176 hf 177 hf values we investigated this problem by attempting to construct mineral and whole rock isochrons for eucrites and angrites meteorites from different parent bodies exhibit similar disturbance features suggesting that a common process is responsible minerals scatter away from isochron regressions for both meteorite classes with low hf phases such as plagioclase and olivine typically being most displaced above or left of reference isochrons relatively hf rich pyroxene is less disturbed but still to the point of steepening lu hf errorchrons using our lu hf and sm nd data we tested various hf and lu redistribution scenarios and found that decoupling of lu hf from 176 hf 177 hf must postdate the accumulation of significant radiogenic 176 hf therefore early irradiation or diffusion cannot explain the excess 176 hf instead disturbed meteorite isochrons are more likely caused by terrestrial weathering contamination or common laboratory procedures the partial dissolution of phosphate minerals may predominantly remove rare earth elements including lu leaving relatively immobile and radiogenic hf behind robust lu hf and improved sm nd meteorite geochronology will require the development of chemical or physical methods for removing unsupported radiogenic hf and silicate hosted terrestrial contaminants without disturbing parent daughter ratios

abundance distribution and origin of 60fe in the solar protoplanetary disk abstract meteorites contain relict decay products of short lived radionuclides that were present in the protoplanetary disk when asteroids and planets formed several studies reported a high abundance of 60fe t1 2 2 62 0 04 myr in chondrites 60fe 56fe 6 10 7 suggesting that planetary materials incorporated fresh products of stellar nucleosynthesis ejected by one or several massive stars that exploded in the vicinity of the newborn sun we measured 58fe 54fe and 60ni 58ni isotope ratios in whole rocks and constituents of differentiated achondrites ureilites aubrites heds and angrites unequilibrated ordinary chondrites semarkona ll3 0 and nwa 5717 ungrouped petrologic type 3 05 metal rich carbonaceous chondrite gujba cba and several other meteorites cv el h ll chondrites iiiab iva ivb iron meteorites we derive from these measurements a much lower initial 60fe 56fe ratio of 11 5 2 6 10 9 and conclude that 60fe was homogeneously distributed among planetary bodies this low ratio is consistent with derivation of 60fe from galactic background 60fe 56fe 2 8 10 7 in the interstellar medium from ray observations and can be reconciled with high 26al 27al 5 10 5 in chondrites if solar material was contaminated through winds by outer layers of one or several massive stars e g a wolf rayet star rich in 26al and poor in 60fe we present the first chronological application of the 60fe 60ni decay system to establish the time of core formation on vesta at 3 7 1 7 2 5 myr after condensation of calcium aluminum rich inclusions cais

petrographic constraints on the diversity of chondrule reservoirs in the protoplanetary disk abstract chondrules from different chondrite groups show characteristic properties including abundances of different chondrule textural types chondrule sizes oxygen isotope compositions chondrule bulk compositions and petrographic properties of type i and type ii chondrules including abundances of relict grains overall it can be argued that each chondrite group sampled a unique chondrule reservoir and that chondrite groups may represent fractions of larger reservoirs that are represented by chondrite classes these observations provide constraints for models of the early solar system in which it is necessary to establish multiple separate chondrule reservoirs and maintain them over extended time periods models for accretion of chondrite parent bodies must be able to account for localized accretion of chondrules that were formed in spatially or temporally separated reservoirs

nickel isotope heterogeneity in the early solar system article i nfo ni of bulk iron and chondritic meteorites carbonaceous chondrites have variable positive e 62 ni 0 05 to 0 25 whereas ordinary chondrites have negative e 62 ni 0 04 to 0 09 the ni isotope compositions of iron meteorites overlap with those of chondrites and define an array with negative slope in the e 60 ni versus e 62 ni diagram the ni isotope compositions of the volatile depleted group ivb irons are similar to those of the refractory co cv carbonaceous chondrites whereas the other common magmatic iron groups have ni isotope compositions similar to ordinary chondrites only enstatite chondrites have identical ni isotope compositions to earth and so appear to represent the most appropriate terrestrial building material differences in e 62 ni reflect distinct nucleosynthetic components in precursor solids that have been variably mixed but some of the e 60 ni variability could reflect a radiogenic component from the decay of 60 fe comparison of the e 60 ni of iron and chondritic meteorites with the same e 62 ni allows us to place upper limits on the 60 fe 56 fe of planetesimals during core segregation we estimate that carbonaceous

mechanism of drying induced rebound movements in a soil slope in sai kung hong kong abstract this paper reports on a study conducted during 1992 1995 on the progressive movement of a slope in sai kung hong kong in spite of the fact that significant downslope movement was triggered during the rainy seasons the field data show that remarkable rebound in the uphill direction was mobilized during dry season when the groundwater level dropped this paper focuses on such rebound deformation which is due to the drying of the soils to investigate the mechanism of the rebound deformation a two dimensional finite element model of the slope was established and a series of hydraulic and mechanical analyses were conducted it is found that the volumetric contractive behaviour caused by the increase in suction within the unsaturated soil zones and the reduction in pore pressure in the submerged soils due to the lowering of groundwater level induced the rebound deformation moreover the water retention properties of the unsaturated soil zones can also strongly influence such deformation