internal fluidization in granular soils internal fluidization the process whereby granular soil is transformed into a fluid like state when liquid or gas is pumped into it is of importance in a number of civil and geotechnical engineering processes for example pipe leakage flow through sheet piling pile jetting and spudcan extraction this paper draws together the limited literature on the subject and identifies the stages in the process by which fluidization occurs using data from small scale experiments and simple analysis factors affecting the onset of fluidization and its development are identified

impact induced frictional melting in ordinary chondrites a mechanism for deformation darkening and vein formation high speed friction experiments have been performed on the ordinary chondrites el hammami h5 s2 and sahara 97001 l6 s3 using an axial friction welding apparatus each sample was subjected to a strain rate of 103 to 104 s 1 which generated 250 to 500 m deep darkened zones on each sample cube thin section analyses reveal that the darkened areas are composed of silicate glass and mineral fragments intermingled with dispersed submicron size feni and fes blebs fracturing of mineral grains and the formation of tiny metallic veins define the extent of deformation beyond the darkened shear zone these features are not present in the original meteorites the shear zones and tiny veins are quite similar to certain vein systems seen in naturally deformed ordinary chondrites the experiments show that shock deformation is not required for the formation of melt veins and darkening in ordinary chondrites therefore the presence of melt veins and darkening does not imply that an ordinary chondrite has undergone severe shock deformation in fact high strain rate deformation and frictional melting are especially important for the formation of veins at low shock pressures

experiment on fluidization in unbounded domains one dimensional fluidization in a bounded domain is a well understood phenomenon however in unbounded domains the formation of an interface between the fluidized and unfluidized regions is a complicated phenomenon that is poorly understood at present this experimental study advances the fundamental understanding of two dimensional fluidization and provides a data base for future numerical modeling the study was performed in a 365 7cm 121 9cm 30 4cm 12ft 4ft 1ft tank filled with sand overlying a small source pipe the back panel contains 143 pressure taps used to determine the hydraulic head distribution for the bed depths tested the lines of constant hydraulic head are horizontal in the fluidized region and curve downward in the unfluidized region the one dimensional theoretical superficial velocity needed to initiate fluidization provides a reasonable approximation of the two dimensional incipient fluidization conditions the average sand concentration in the fluidized region decreases with incr

alkali feldspathic material entrained in fe s rich veins in a monomict ureilite the elephant moraine eet 96001 ureilite contains a remarkable diversity of feldspars which occur as tiny no more than 60 m maximum dimension grains within a few fe s rich now weathered to mostly fe oxide veins molar s fe ratio in the veins averages 0 08 0 02 the veins meander and feature large fluctuations in apparent width they appear to have entered this monomict breccia by a gentle percolative process not by violent impact injection the feldspars are accompanied by a diverse suite of k rich and generally also ti rich feldspathic glasses and also major proportions of silica and pyroxene which is largely fassaitic a rhnite like phase is also found and as inclusions in one of the fassaites a cr poor spinel like phase the feldspars mostly feature remarkably high k na compared to feldspars of comparable an from polymict ureilites the eet 96001 feldspathic component was probably once part of a thin basaltic crust on a ureilite asteroid the spinel included in one of the fassaites formed at remarkably high fo2 apparent oxidation state of iron 41 atom fe3 suggesting that the parent magma possibly assimilated near surface water however the fe3 was not directly measured and has conceivably been affected by terrestrial weathering also there is no assurance that this fassaite originated together with the typical feldspar we speculate that the feldspathic component was mixed into the dense fe s rich vein material and very soon thereafter the fe s rich vein material was emplaced adjacent to the eet 96001 host ureilite at an advanced stage in a chaotic catastrophic disruption and partial reassembly process that affected all ureilites the high k nature of the eet 96001 feldspathic component including the feldspathic glasses suggests that fractional fusion may not have been as common during ureilite anatexis as has been inferred from recent studies of clast assemblages in polymict ureilites

petrology of the indian eucrite piplia kalan piplia kalan is an equilibrated eucrite consisting of 60 80 vol lithic clasts in a subordinate brecciated matrix ophitic subophitic clasts fall into two groups finer grained lithology a and coarser grained lithology b very fine grained clasts with equigranular textures lithology c also occur and originally were hypocrystalline in texture the variety of materials represented in piplia kalan suggests cooling histories ranging from quenching to slower crystallization despite textural differences clasts and matrix have similar mineral and bulk compositions thus piplia kalan is probably best classified as a genomict breccia that could represent fragments of a single lava flow or shallow intrusive body including fine grained or glassy outer margin and more slowly cooled coarser grained interior bulk composition suggests that the meteorite is most closely related to the main group eucrites but it probably was affected by minor amounts of fractional crystallization piplia kalan displays evidence of an early shock event including brecciated matrix and areas of lithic clasts that contain very fine grained granular pyroxene between deformed feldspar laths the meteorite also displays evidence of at least one episode of extensive thermal metamorphism hypocrystalline materials are recrystallized to hornfelsic textures and minerals throughout the meteorite contain abundant inclusions that are relatively large in size veins of brown glass transect both clasts and matrix and indicate a second postmetamorphism shock event

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

genesis and environmental significance of a buried middle pleistocene soil in eastern england abstract a middle pleistocene soil in eastern england developed in fluvial and intertidal sediments and buried beneath till deposits was studied using macromorphological physical chemical and micromorphological techniques the major pedogenic processes active in its formation were clay illuviation rubification gleying mineral weathering and cryogenic disruption a development sequence for the soil was proposed on the basis of superposition of various macro and micromorphological features three phases of clay illuviation were identified with periods of intense disruption occurring between and after the second and third phases the second phase of disturbance was related to cryogenesis during the early anglian stage of the british ouaternary succession illuvial clay coatings were fragmented or deformed and duplex textural lamellae a features developed more large scale disruption followed to form periglacial involutions and small contraction cracks the latter being infilled with translocated silt at some stage the eluvial horizon was eroded and coversand began to be deposited a gradual change to a more arid permafrost environment led to development of sand wedges as the anglian glacier advanced the soil was glacitectonically deformed and buried beneath till later melting of the permafrost led to deformation of the larger sand wedges

39ar40ar age and petrology of chico large scale impact melting on the l chondrite parent body our studies of the 105 kg chico l chondrite show that it contains 60 impact melt and the largest volume of impact melt recognized in stony meteorites we suggest that it is part of a much larger dike complex that formed when chondritic impact melt was intruded into host chondrite during a large if not catastrophic impact on the l chondrite parent body at about 0 5 ga petrologic and 39ar 40ar dating studies were made on several lithologies including the massive melt zone host chondrite and melt chondrite boundaries for the purpose of studying the melting and thermal histories associated with impacts on small bodies and their effects on the k ar chronometer the chondritic host is shocked to stage s6 and contains pockets and veins of melt there are no unmelted clasts in the interior of the melt coalesced metal troilite nodules reach up to 2 cm in size melt near the contact with the host chondrite contains numerous clasts and quenched more rapidly metal troilite textures suggest cooling rates of 0 1 c s in the interior of the melt dike during crystallization secondary kamacite rims indicate cooling at 0 01 1 c y over the range of 700 500 c consistent with an impact heated volume of up to a kilometer in thickness compositions of olivines and pyroxenes are generally similar in melt and chondritic host reflecting rapid crystallization not metamorphic equilibration the interior melt shows an overall depletion in k whereas the melt near the boundary is enriched in k the 39ar 40ar release spectra during stepwise heating of both melt and chondrite samples can be divided into two parts based on ar diffusion properties and k ca ratios the low temperature high k ca phase of both melt and host chondrite show ages of 0 54 0 78 ga ages of the high temperature low k ca phase of the melt are comparable or higher 0 61 1 35 ga whereas those of the host chondrite are even higher 0 87 1 86 ga due to lesser degrees of degassing isochron plots for several melt samples suggest an age of 0 53 ga and the presence of variable amounts of excess 40ar not completely degassed by the impact even this age however is significantly higher than the previously reported rb sr isochron age of 0 467 015 ga the apparent retention of radiogenic 40ar in the chico impact melt in spite of its relatively large size absence of clasts and moderately slow cooling rate below 700 c raises questions as to the reliability of using melts for 39ar 40ar dating of meteoritic impact events

palaeoenvironmental and stratigraphic significance of the valley farm and barham soils in eastern england abstract the valley farm and barham soils are important stratigraphic units representing an early and or middle pleistocene depositional hiatus within parts of eastern england the barham soil buried beneath anglian sediments is recognised by a variety of large and small scale cryogenic features which developed in cromerian sediments or were superimposed upon the valley farm soil during the early anglian the valley farm soil is rubified mottled and contains substantial quantities of translocated clay originally attributed solely to temperate cromerian stage pedogenesis its stratigraphic status has changed over recent years as the age range of its kesgrave sands and gravels parent material has been extended currently the valley farm soil is regarded as a complex stratigraphic unit with component soils developed on a series of different age surfaces perhaps spanning cold and temperate intervals over more than a million years detailed micromorphological studies of the valley farm soil on some of these surfaces have confirmed its variable pedological complexity a number of theoretical and practical problems however need to be confronted and solved before its pedological record can be used routinely to provide an independent means of dating and reconstructing detailed palaeoenvironments

physical modelling of pile drilling in sand drilling for foundation piles and tieback anchors through soils using a continuous casing to support the borehole is often referred to as overburden drilling monitoring data from several case st

spatial soil variability in the cajon pass chronosequence implications for the use of soils as a geochronological tool abstract spatial variation of soil properties on a single geomorphic surface has a significant influence on surface correlations and age determinations made on the basis of soil properties few chronosequence studies have been based on a sufficient number of soils to evaluate the influence of soil variability we described and evaluate 35 soils on four terrace surfaces which constitute part of a previously described well dated soil chronosequence in cajon pass in southern california soils were described on both bar and swale sites removed from the influence of deposition adjacent slopes the influence of eolian silt on the rate of pedogenesis in cajon pass indicates that this sequence of soils cannot be considered a chronosequence in the strict sense of the term furthermore the evidence for a pedogenic threshold in these soils indicates that the soils do not develop monotonically with time and that soil development cannot be defined by a continuous univariant chronofunction the discrete nature of the data from a chronosequence and the complex nature of soil development are better analyzed by multivariate statistical procedures systematic variation in soil properties between soils from bar sites and soils from swale sites is attributed to geomorphic processes which affect either the rate or duration of eolian dust accumulation soils from bar sites were less variable and generally less strongly developed that soils from swale sites from the same surface the degree of variation of soil properties determined for a given landscape position on a surface is sufficient to raise questions concerning the usefulness of chronofunctions for determining the nature of time dependent pedogenic changes and for providing numerical age determinations multivariate statistical methods were used to differentiate among soils developed on three surfaces which differ in age by only 1500 years

thames river sediments of the british early and middle pleistocene abstract the thames drainage system contains the most complete record of fluvial sediments in the british quaternary the kesgrave sands and gravels form the main body of this sediment having been deposited over an interval that spans the later part of the early pleistocene and most of the middle pleistocene conventional stages pre pastonian a through to early anglian ca 1 2 ma this deposit provides a stratigraphic context for related bio morpho and pedostratigraphic evidence and for the recognition of pre anglian pre oi stage 12 upland glaciation in the welsh mountains and intense periglaciation in lowland england it also facilitates correlation with the stratigraphy of northern europe and the global pattern of orbitally forced climatic change this paper describes the first catchment wide correlation of thames river sediments and proposes a formal redefinition of the lithostratigraphic units concerned the scheme outlined here is based on two lithologically distinctive formations defined at type areas reflecting significant changes in catchment dimensions the earlier sudbury formation was formed when the thames catchment extended into wales and drained northwards across east anglia the later colchester formation was formed after the upper catchment had been reduced in extent to that of the present river but continued to flow across east anglia the whole sediment body is now named the kesgrave group

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

pseudotachylyte controversy fact or friction high speed slip experiments performed on westerly granite using friction welding apparatus reveal that comminution is an essential precursor to melting by friction observations of slip surfaces via analytical scanning electron microscopy sem document the following sequence of events occurring in 2 s with increasing velocity up to 2 m s fracture progressive comminution surface melting of mineral fragments fragment to fragment adhesion and finally production of a fragment laden melt supported suspension explosive dehydration and melting of the epidote group mineral allanite indicates that temperatures of at least 1000 c were realized at the interface this is corroborated by calculation of the temperature rise for the known operating conditions contrary to earlier proposals these results show that comminution and frictional melting are complementary and not mutually exclusive processes depending on the velocity shear stress displacement relations prevailing during frictional slip rocks produced in seismogenic zones can be predominantly comminuted wall rock or fragment melt mixes pseudotachylytes

possible fluid rock interactions on differentiated asteroids recorded in eucritic meteorites the eucritic meteorites are basaltic rocks that originate from the upper part of the crust of some small bodies as exemplified possibly by asteroid 4 vesta a few eucrites appear to have been modified by different degrees of a late stage alteration process that caused significant variations in mineralogy three distinct alteration stages are identified 1 fe enrichment along the cracks that cross cut the pyroxene crystals fe metasomatism secondary olivine and minute amounts of troilite are found only occasionally in cracks at this stage 2 deposits of fe rich olivine fa64 86 and minor amounts of troilite are frequent inside the cracks sporadic secondary ca rich plagioclase an97 98 is associated with the fayalitic olivine 3 at this stage the fe enrichment of the pyroxene is accompanied by a marked al depletion moreover secondary ca rich plagioclase is more frequent and partly fills some cracks or rims of the primary plagioclase crystals the composition of the secondary phases on one hand the lack of incompatible trace element enrichment in the metasomatized pyroxenes on the other hand rule out a silicate melt as the metasomatic agent although no hydrous phase has been yet identified in the studied samples aqueous fluids are plausible candidates for explaining the deposits of ferroan olivine and anorthitic plagioclase inside the fractures of the studied unequilibrated eucrites

metamorphic history of the eucritic crust of 4 vesta the petrologic properties of eucrites indicate that most formed as rapidly cooled lava flows that were subsequently metamorphosed at 800 c for periods of about 1 myr we have modeled the development of the eucritic crust of the eucrite parent body assumed to be asteroid 4 vesta by the eruption and subsequent burial of lava flows serial magmatism the burial of the flows causes them to reheat to metamorphic temperatures 800 c provided that the initial thermal gradient in the upper 5 km was steep as it would be if 26al was the heat source our model shows that most eucrites were metamorphosed for periods over 1 myr in a crust between 15 and 25 km thick if volcanism lasted only 1 to a few myr longer periods of volcanism do not result in high enough peak metamorphic temperatures to be consistent with eucrite data the hot lower crust in vesta provides an environment in which even small few meters dikes could have cooled slowly enough to produce cumulate eucrites and possibly diogenites

common asteroid break up events of eucrites diogenites and howardites and cosmic ray production rates for noble gases in achondrites we determined the cosmic ray produced noble gas abundances in eight diogenites four eucrites and four howardites using these and additional noble gas and chemical data from the literature composition and shielding dependent production rates of achondrites for 3he 21ne 38ar 78kr 83kr and126xe were derived based on 81krkr exposure ages the cosmogenic ratio 22ne 21ne is found to be a valid shielding indicator for all howardites eucrites and diogenites heds this ratio correlates with other shielding dependent ratios such as 78kr 83kr 80kr 83kr 124xe 131xe 126xe 131xe and 128xe 131xe we show that strong correlations for these ratios also exist for basaltic lunar rocks the new production rates were used for the calculation of exposure ages for all heds with known noble gas abundances two major exposure age clusters at 21 ma and 38 ma are observed in all three classes we find that five asteroid break up events characterized by exposure ages 6 1 ma 12 2 ma 21 4 ma 38 8 ma and 73 3 ma produced all diogenites fifteen out of seventeen howardites and twenty eight out of thirty nine eucrites we conclude that asteroidal or cometary impact events at such times on one or several parent bodies are responsible for the ejection of eucrites howardites and diogenites probable parent bodies are multiple 4 vesta derived kilometer sized objects of basaltic achondritic composition reaching the 3 1 resonance region a proposed source area for meteorites the direct ejection from vesta and capture by earth of basaltic meteorites has been shown to be dynamically difficult in such a scenario large events 38 ma and 21 ma ago are required liberating simultaneously material representing vesta s surface eucrites howardites and interior regions diogenites

ordinary mesostasis and not so ordinary symplectites late stage assemblages in howardites abstract two categories of symplectites have been observed in howardites three phase composed of vermicular intergrowths of ferroan augite fayalitic olivine and silica and two phase composed of vermicular intergrowths of orthopyroxene and troilite three phase symplectites have been previously shown to represent the breakdown products of metastable pyroxene in howardites they appear to be genetically related to gabbroic eucrites in some cases and under yet to be specified conditions ferroan clinopyroxene in gabbroic eucrites may undergo only localized decomposition resulting in oriented exsolution like features breakdown phases in those cases are fayalitic olivine silica and depending on the mgo content of the system orthopyroxene as opposed to three phase symplectites two phase symplectites are most likely of diogenitic origin they probably formed via impact induced localized melting of diogenitic orthopyroxene in the presence of troilite grain boundary melting three phase symplectites in howardites occasionally contain accessory amounts of ilmenite troilite and or kamacite and are exclusively associated with medium grained feo rich pyroxene silica and plagioclase all minerals involved are late stage crystallites or mesostasis phases in general highly evolved eucritic lithologies constitute only a minor fraction of howardites however considering that three phase symplectites are generated in a low pressure i e near surface environment feo and cao rich eucritic rocks may be exposed locally on vesta s surface this in turn is highly relevant to the ongoing dawn mission

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

glass veins in the unequilibrated eucrite yamato 82202 the unequilibrated eucrite yamato 82202 y82202 contains a network of relatively thick up to 1 mm in width glass veins the host of the meteorite represents a monomict breccia composed of volcanic rock that crystallized 4 3 ga ago as a lava flow on the surface of 4 vesta the veins formed 3 90 0 04 ga ago probably as a result of frictional melting associated with impact under conditions of low effective oxygen fugacity and higher sulfur fugacity the glass contains disordered structural elements characteristic of pyroxene and feldspar reminiscent of the eucritic target lithology the unequilibrated pyroxenes of the volcanic host and the pristine character of the glass indicate that this meteoritic material did not experience significant thermal metamorphism after initial crystallization of the lava hence it was not affected by regional metamorphism caused by burial to a significant depth or by long term contact metamorphism associated with a thick lava flow large intrusion or hot layer of impact ejecta the meteorite resided at a shallow depth though not at the surface on 4 vesta or on one of the vestoids until it was ejected and traveled to earth probably with other hed materials that have 36ar exposure ages of 13 ma these data suggest that the surface of the asteroid 4 vesta has significant though probably small proportions of glass as well as unequilibrated volcanic rock

experimental observations on the initiation of sand bed erosion by an upward water jet abstracterosion of a saturated sand bed by a vertically upward water jet was studied experimentally direct observations on the behavior of sand bed erosion were obtained by increasing the flow rat

vesta vestoids and the howardite eucrite diogenite group relationships and the origin of spectral differences spectra of asteroid 4 vesta and 21 small estimated diameters less than 10 km asteroids with vesta like spectral properties vestoids were measured at visible and near infrared wavelengths similar to0 44 to similar to1 65 mum all of the measured small asteroids except for 2579 spartacus have reflectance spectra consistent with surface compositions similar to eucrites and howardites and consistent with all being derived from vesta none of the observed asteroids have spectra similar to diogenites we find no spectral distinction between the 15 objects tabulated as members of the vesta dynamical family and 6 of the 7 sampled non family members that reside just outside the semi major axis a eccentricity e and inclination i region of the family the spectral consistency and close orbital a e i match of these non family objects to vesta and the vesta family imply that the true bounds of the family extend beyond the subjective cut off for membership asteroid 2579 spartacus has a spectrum consistent with a mixture of eucritic material and olivine spartacus could contain olivine rich material from vesta s mantle or may be unrelated to vesta altogether laboratory measurements of the spectra of eucrites show that samples having nearly identical compositions can display a wide range of spectral slopes finer particle sizes lead to an increase in the slope which is usually referred to as reddening this range of spectral variation for the best known meteoritic analogs to the vestoids regardless of whether they are actually related to each other suggests that the extremely red spectral slopes for some vestoids can be explained by very fine grained eucritic material on their surfaces

a new source of basaltic meteorites inferred from northwest africa 011 eucrites are a class of basaltic meteorites that share common mineralogical isotopic and chemical properties and are thought to have been derived from the same parent body possibly asteroid 4 vesta the texture mineralogy and noble gas data of the recently recovered meteorite northwest africa nwa 011 are similar to those of basaltic eucrites however the oxygen isotopic composition of nwa011 is different from that of other eucrites indicating that nwa011 may be derived from a different parent body the presence of basaltic meteorites with variable oxygen isotopic composition suggests the occurrence of multiple basaltic meteorite parent bodies perhaps similar to 4 vesta in the early solar system

the south african polymict eucrite macibini the polymict eucrite macibini is a fragmental breccia predominantly composed of eucritic materials with minor proportions maximum 2 vol of diogenitic material hence it is intermediate between the yamato 74159 type polymict eucrites which contain negligible amounts of magnesian orthopyroxene and the howardites the present study provides mineralogical and bulk compositional data for the meteorite breccia and for six clasts these clasts include both volcanic and igneous rocks and a variety of impact generated rocks a broad range of degrees of postcrystallization metamorphism affected these materials before the final aggregation of the breccia clast a is a fragment of unequilibrated eucrite with subophitic texture the edges of the zoned pyroxenes in this clast are composed of a host of fe rich augite containing vermicules blebs and lamellae composed of a mixture of fe rich olivine and silica similar features occur as fragments in lunar breccias and are attributed by some workers to the breakdown of pyroxferroite an fe rich pyroxenoid however textures and compositions of these augite olivine silica intergrowths in clast a suggest that in this case they are the result of decomposition in a series of steps of fe rich subcalcic augite among the fragments of impact generated material in macibini is clast 2 an earlier formed clastic breccia that was lithified before being broken apart and included in the meteorite breccia clast 3 is an impact melt breccia that is composed of rock and mineral fragments in a devitrified groundmass clast c is also an impact melt breccia that has a coarser grained hornfelsic groundmass that resulted from extensive metamorphism after formation

development of a feldspar weathering index and its application to a buried soil chronosequence in southeastern england abstract an index of feldspar weathering ifw has been developed based upon the assignment of individual grains to weathering classes defined in terms of progressive changes in surface morphology identifiable under a polarising microscope the index was used to test the hypothesis that profiles of a buried paleosol developed on the higher terraces of the river thames in southeastern england are more weathered than those formed on lower and younger terrace surfaces ifwr ratio between the ifw of soil and parent material and ifwd difference between the ifw of soil and parent material values support a trend of increased weathering with assumed terrace age although the pattern is less clear and conclusive towards the base of the terrace sequence anomalies in the dataset can be attributed to a range of factors including the possible variable composition and structure of the feldspars the nature of the parent material samples and probable fluctuations in soil processes and environments over time notwithstanding these problems some of which are specific to the study reported here the technique and general approach clearly have more widespread potential for the semi quantitative comparison of the relative weathering statuses of soils

smyer h chondrite impact melt breccia and evidence for sulfur vaporization smyer is an h chondrite impact melt breccia containing 20 vol 0 5 to 13 mm thick silicate rich melt veins surrounding unmelted subrounded chondritic clasts up to 7 cm in maximum dimension at the interface between some of the melt veins and chondritic clasts there are troilite rich regions consisting of unmelted crushed 0 2 to 140 m size angular silicate grains and chondrule fragments surrounded by troilite and transected by thin troilite veins troilite fills every available fracture in the silicates including some as thin as 0 1 m little metallic fe ni is present in these regions the fes fe modal ratio ranges from 25 1 to 500 1 far higher than the eutectic weight ratio of 7 5 1 the texture of these regions indicates that the sulfide formed from a fluid of very low viscosity the moderately high viscosity 0 2 poise and large surface tension of liquid fes its inability to wet silicate grain surfaces at low oxygen fugacities and the supereutectic fes fe ratios in the troilite rich regions indicate that the fluid was a vapor it seems likely that during the shock event that melted smyer many silicates adjacent to the melt veins were crushed upon release of shock pressure some of the troilite evaporated and dissociated molecules of s2 were transported and condensed into fractures and around tiny silicate grains there they combined with fe from small adjacent metallic fe ni grains to form troilite the ni content at the edges of some of these metal grains increased significantly co from these ni rich grains diffused into nearby kamacite impact induced s volatilization may have played a major role in depleting the surface of 433 eros and other chondritic asteroids in s

survey and evaluation of eucrite bulk compositions the purpose of this survey is to establish reference bulk elemental abundances for the eucrites and thereby provide the basis to test core formation models as well as partial melting fractional crystallization and magma ocean theories for the eucrite parent body in order to evaluate bulk elemental abundances for the eucrites 296 peer reviewed articles monographs theses or books and 143 abstracts dating from 1938 to 1997 were surveyed of the 101 eucrites having at least one set of elemental abundance analyses reported in the literature 20 were selected for in depth examination the selection criteria of our sample were based on the total number of analyses available for a given eucrite and the total number of elements for which data exist the mean bulk elemental abundance 1 standard deviation and the percent deviation were calculated for each element in a given eucrite in order to evaluate the quality of the mean abundances the elements were then grouped according to availability of data and percent deviations possible reasons for the different deviations in the different groups are briefly discussed from the major element abundances the normative cipw composition the molar compositions of pyroxene olivine and plagioclase and the bulk densities were calculated and compared to petrographic observations the calculated norms for the noncumulates agree well with the observations while the norms for the cumulates do not possible reasons for this are discussed unfortunately analyses of many elements are poorly represented in the literature and many bulk analyses suffer from unacceptable levels of uncertainty therefore future work requires bulk elemental analyses for some of the more poorly characterized elements in eucrites especially those of key elements used for planetary modeling

global crustal metamorphism of the eucrite parent body abstract we conducted a petrologic study of 18 equilibrated eucrites with the goal of understanding the formation and evolution of the crust of asteroid 4 vesta the likely source of eucrite meteorites their textures indicate that eucrites were basaltic igneous rocks but modified by postcrystallization brecciation recrystallization and impact melting recrystallized rocks are the most common among clasts in the eucrites impact melt breccias are rare equilibration temperatures of the metamorphic clasts range from 700 to 1000 c with most in the 800 900 c range complex exsolution and recrystallization textures in pyroxenes suggest that eucrites cooled very slowly from high peak temperatures after reheating this extended period of thermal metamorphism requires a high interior temperature in a vesta sized body this metamorphism could have taken place during and shortly after crust formation we suggest the crust of vesta evolved through the eruption rapid cooling and subsequent burial and reheating of lava flows as the crust grew in thickness the depth of burial increased causing temperatures to rise and leading to global metamorphism this resulted in only a small percentage of unequilibrated eucrites only the last few percent of basalts erupted would not be metamorphosed and a wide range of metamorphic temperatures and durations for the equilibrated eucrites

the role of gas fluidisation in the formation of massive volcaniclastic kimberlite abstract massive volcaniclastic kimberlite mvk deposits are a volumetrically important constituent in most kimberlite diatremes mvks are typically characterised by their uniform texture and homogeneous composition and previous studies suggest that they exhibit little appreciable internal variation however new field results from the venetia k1 diatreme south africa show that mvk displays significant changes over metre scales the textural characteristics and large and small scale structure of the deposits are described and interpreted as being due to fluidisation laboratory experiments of tapered fluidised beds demonstrate how they are heterogeneous with fluidisation and mixing limited to the centre of the bed marginal wedge shaped regions remain unfluidised the unfluidised regions are internally laminated and slip downwards when a high proportion of the bed is fluidised the observations also demonstrate how fluctuations in gas velocity can produce steep internal boundaries between laminated and well mixed regions data consistent with gas fluidisation in mvk deposits includes the massive structure uniform distribution of lithic clasts presence of steep internal contacts dominantly sub vertical crystal fabrics across the vent occurrence of surface derived material along the tapered diatreme walls and the presence of degassing structures we propose that the overall structure of the venetia k1 diatreme fill is consistent with a multi stage fluidised emplacement which involved 1 strong initial fluidisation that caused thorough mixing of juvenile and lithic material 2 a gradual step wise decrease in gas flux that produced nested pipe like sequences and 3 migration of the narrow fluidised column towards the steep eastern diatreme wall the occurrence of 4 degassing structures in mvk deposits across the vent is consistent with an overall rapid transition from high to low degrees of fluidisation towards the end of the eruption

isotopic and petrographic evidence for young martian basalts radiometric age data for shergottites yield ages of 4 0 ga and 180 575 ma the interpretation of these ages has been and remains a subject of debate here we present new 39 ar 40 ar laser probe data on lherzolitic shergottites allan hills alh 77005 and northwest africa nwa 1950 these two meteorites are genetically related but display very different degrees of shock damage on a plot of 40 ar 36 ar versus 39 ar 36 ar the more strongly shocked alh 77005 45 55 gpa does not yield an array of values indicating an isochron but the data are highly scattered with the shock melts yielding 40 ar 36 ar ratios of 1600 2026 apparent ages calculated from these extractions range from 374 8183 ma with 50 of the data particularly from the shock melts yielding impossibly old ages 4 567 ga on the same plot extractions from igneous minerals in the less shocked nwa 1950 30 44 gpa yield a fitted age of 382 36 ma argon extractions from the shock melts are well distinguished from minerals with the melts exhibiting the highest 40 ar 36 ar ratios 1260 1488 and the oldest apparent ages laser step heating was also performed on maskelynite separates from nwa 1950 yielding ages of 1000 ma at the lowest release temperatures and ages of 360 and 362 ma at higher temperature steps stepped heating data from previous studies have yielded ages of 500 and 700 ma to 1 7 ga for alh 77005 maskelynite separates if the ages obtained from igneous minerals represent undegassed argon from an ancient 4 0 ga rock then the ages are expected to anticorrelate with the degree of shock heating the data do not support this inference our data support young crystallization ages for minerals and martian atmosphere as the origin of excess 40 ar in the shock melts the shock features of shergottites are also reviewed in the context of what is known of the geologic history of the martian surface through remote observation the oldest most heavily cratered surfaces of mars are thought to be 4 0 ga we contend that ancient rocks from mars noachian 3 5 ga are likely to record multiple impact events reflecting megaregolith formation and the cumulative effects of erosion and aqueous alteration occurring during or since that era young rocks late amazonian 0 6 ga should record a relatively simple history of emplacement and ejection from the near surface we show that although shergottites are strongly shocked they are relatively pristine crystalline igneous rocks and not pervasively altered breccias the petrography of shergottites is at odds with an ancient age interpretation a model in which young coherent rocks are preferentially sampled by hypervelocity impact because of material strength is considered highly plausible

oxygen isotopic constraints on the origin and parent bodies of eucrites diogenites and howardites abstract a few eucrites have anomalous oxygen isotopic compositions to help understand their origin and identify additional samples we have analyzed the oxygen isotopic compositions of 18 eucrites and four diogenites except for five eucrites these meteorites have 17o values that lie within 2 of their mean value viz 0 242 0 016 consistent with igneous isotopic homogenization of vesta the five exceptional eucrites nwa 1240 pasamonte both clast and matrix samples pca 91007 a 881394 and ibitira have 17o values that lie respectively 4 5 5 15 and 21 away from this mean value nwa 1240 has a 18o value that is 5 below the mean eucrite value four of the five outliers are unbrecciated and unshocked basaltic eucrites like nwa 011 the first eucrite found to have an anomalous oxygen isotopic composition the fifth outlier pasamonte is composed almost entirely of unequilibrated basaltic clasts published chemical data for the six eucrites with anomalous oxygen isotopic compositions including nwa 011 exclude contamination by chondritic projectiles as a source of the oxygen anomalies only nwa 011 has an anomalous fe mn ratio but several anomalous eucrites have exceptional na ti or cr concentrations we infer that the six anomalous eucrites are probably derived from five distinct vesta like parent bodies pasamonte and pca 91007 could come from one body these anomalous eucrites like the isotopically normal unbrecciated eucrites with 4 48 gyr ar ar ages are probably deficient in brecciation and shock effects because they were sequestered in small asteroids 10 km diameter during the late heavy bombardment following ejection from vesta like bodies the preservation of vesta s crust and the lack of deeply buried samples from the hypothesized vesta like bodies are consistent with the removal of these bodies from the asteroid belt by gravitational perturbations from planets and protoplanets rather than by collisional grinding

etch pit size and shape distribution on orthoclase and pyriboles in a loess catena abstract etch pits on 50 100 m orthoclase and pyribole grains from the e b and c horizons of a catena or drainage sequence of well drained somewhat poorly drained and poorly drained loessal soils were analyzed using sem and digital image analysis the objective was to determine the influence of soil drainage conditions and the associated geochemical environments on dissolution of primary silicates as determined from the distribution of etch pits on the grain surfaces etch pit size frequency distributions indicated that the poorly drained soil contained the smallest and most numerous etch pits for both minerals this indicated low growth rates for etch pits in the poorly drained soil analysis of etch pit shapes indicated that etch pits on pyriboles were more elongated and irregular in the poorly drained soil possibly resulting from a greater growth rate whereas etch pits on orthoclase grains were more elongated and irregular in the well drained soil the larger more elongated and irregularly shaped etch pits on orthoclase from the well drained soil indicative of a greater pit growth rate is consistent with a flushing model of mineral weathering in soils the etch pit size distribution on pyriboles is consistent with the flushing concept but the shape data indicates that other mechanisms of weathering may be involved

sims pb pb and u pb age determination of eucrite zircons at 5 μm scale and the first 50 ma of the thermal history of vesta eucrites a subgroup of basaltic achondrites represent the remnants of the earliest magmatic stage of the solar system formation possibly on the asteroid 4 vesta the precise determination of their crystallization age is therefore important for constraining the evolutionary history of the asteroid including melting and differentiation processes of the parent body zircons would be the best mineral for such purpose however extra terrestrial zircons are rare and those found in eucrites are typically small 5 m using a cameca ims 1280 high resolution ion microprobe precise uranium lead u pb and pb pb ages of the non cumulate basaltic eucrite zircons in bereba cachari caldera camel donga and juvinas were determined successfully at scale of 5 m we obtained a weighted average 207pb 206pb age of 4541 11 ma and u pb concordia age of 4525 24 ma for the five eucrite samples studied a synthesis of available age data of howardites eucrites and diogenites indicate a protracted magmatic history on vesta with a most pronounced core mantle differentiation event marked at 4564 2 ma followed by a peak of basaltic magmatism at 4552 7 ma which gradually diminished over the next 50 ma thermal modeling of vesta suggests that partial melt fraction of greater than 10 with temperature well exceeding 1500 k could be maintained over this period throughout its interior this is consistent with the chronological records of eucrites suggesting persistent magmatism on vesta during the first 50 ma in the early solar system

the role of fluidisation in the formation of volcaniclastic kimberlite grain size observations and experimental investigation abstract deep steep sided kimberlite pipes in southern africa are normally partially filled with multiple units of a characteristically massive structureless volcaniclastic rock here termed massive volcaniclastic kimberlite mvk these units can be arranged in a pseudo concentric nested pipes within pipes structure several key observations on typical mvk from the venetia kimberlite pipes south africa indicate that fluidisation may have been an important process during its emplacement these include 1 the thorough mixing together of juvenile components and of lithic components derived from all stratigraphic levels of the country rock and 2 a matrix composed of void filling minerals related to hydrothermal metamorphism mainly diopside and serpentine which indicates that the primary deposit had a high porosity 50 and 3 particle size distributions poor in fine ash 10 cm analogue experiments utilising a sand bed laced with marker horizons were conducted in order to investigate the role of fluidisation in the formation of mvk high pressure gas fed through the bed from a point source resulted in the formation of an upwardly diverging pipe structure of thoroughly mixed fluidised material bounded by undisturbed sand strong upward gas flow along the centre of the pipe is characteristically bubbly and results in internal circulation with downward moving regions at the pipe margins analysis of the experimental results suggests that the gas velocity decreases linearly with height and has a gaussian distribution of vertical velocity in the cross flow direction a decrease in the gas flow rate resulted in the development of nested pipes reminiscent of the pipes within pipes structures in kimberlite pipes the results suggest that fluidisation could be a major control on the structure and sorting of deposits in kimberlite pipes we propose that the fluidisation of particles in a kimberlite pipe occurs during the final stages of the eruption when erupting pyroclasts and incorporated fragmented lithic material can no longer be ejected out of the deep wide conduit this bed is subject to quasi sustained fluidisation by the erupting gas particle flow which imparts on it the distinctive characteristics of a massive well mixed poorly sorted deposit

impact melting of the cachari eucrite 3 0 gy ago both the host phase and glass veins of the cachari eucrite have been analyzed by microprobe and neutron activation analysis for their chemical compositions and by mass spectrometry for their 39ar 40ar gas retention ages cachari is chemically similar to other non cumulate eucrites the vesicular glass veins vary from pure glass to devitrified glass to areas that are substantially crystalline the glassy areas have nearly the same concentrations of major and trace elements as the unmelted portions of cachari but some differences probably due to preferential dissolution occur along melt contacts the glass formed by shock melting of cachari host or of rock identical to it 39ar 40ar data for the host and glass suggest distinctly different ages of 3 04 07 gy and 3 47 04 gy respectively the time of glass formation which may also be the time of brecciation is most likely given by the 3 0 gy age of the host the higher age for the glass is interpreted to represent incomplete ar degassing during the 3 0 gy event due to the greater resistance to ar diffusion shown by the glass compared to the host event ages significantly younger than 4 5 gy have now been determined for several eucrites and howardites and suggest a long dynamic regolith history for the parent body

record of s rich vapors on asteroid 4 vesta sulfurization in the northwest africa 2339 eucrite in the northwest africa nwa 2339 eucrite a few high fe pigeonite fragments were partially replaced by fine grained troilite mg rich augite silica with minor ilmenite and mg rich ferrosilite the relict pigeonite has distinctly lower fe mn values 17 18 than those 30 of augite and mg rich ferrosilite in the fine grained replacement textures and other eucritic pyroxenes in nwa 2339 the few plagioclase grains associated with these fe rich pigeonite fragments contain high albite components ab17 31 similar replacement textures are also present in a lithic clast consisting of pyroxene and na rich plagioclase ab20 25 in this lithic clast high fe subcalcic augite was replaced by troilite mg rich hedenbergite silica and minor ilmenite whereas mg rich pigeonite remains intact troilite also occurs as tiny inclusions in porous regions of plagioclase moreover the porous regions of plagioclase are enriched in si and depleted in al ca and na compared to relict plagioclase these textures indicate that the formation of troilite rich mineral assemblages is related to the reaction between fesio3 component in pyroxene and s rich vapors whereas the formation of tiny troilite in porous regions of plagioclase is related to the reaction between fe2 in plagioclase and s rich vapors x ray mapping results reveal that during sulfurization of pyroxene and plagioclase lithophile elements mn al ca na and mg were removed to various extents very likely by the s rich vapors based on our observations the s rich vapors could be dry s o p vapors which most likely have been formed by volatilization of pre existing s p bearing materials due to impact heating on the surface of asteroid 4 vesta