ce anomalies in the lew85300 eucrite evidence for ree mobilization during antarctic weathering abstract there is abundant evidence for widespread ree mobilization in antarctic eucrites resulting in ce and eu anomalies and lower whole rock ree abundances relative to typical eucrites using secondary ion mass spectrometry sims we investigated the microdistribution of ce anomalies in the antarctic polymict eucrite lew85300 ce anomalies positive and or negative are present in all three of the minerals plagioclase pyroxene and silica analysed the anomalies occur in grains from all four clasts as well as in mineral and lithic fragments from the surrounding matrix thus there appears to be no lithologic association silica which has been heavily shocked and altered exhibits a lree enriched pattern with negative ce and eu anomalies consistent with a derivation of the ree from ca phosphate dissolution trivalent ree are leached from the phosphates with preferential retention of tetravalent ce and redeposited on silica pyroxene is also widely affected by ree mobilization due to an extensive shock induced microcrack network along cleavage planes a tendency for the largest ce anomalies to occur at low lree concentrations suggests that pyroxene itself experienced ree leaching with concomitant ce retention ce anomalies are rare in plagioclase because this mineral lacks an extensive network along which ree can be mobilized the widespread ree mobilization and evidence for other forms of weathering requires that trace element data be used cautiously especially for antarctic eucrites

oxygen isotope studies of achondrites abstract oxygen isotope abundances provide a powerful tool for recognizing genetic relationships among meteorites among the differentiated achondrites three isotopic groups are recognized l snc mars 2 earth and moon and 3 hed howardites eucrites diogenites the hed group also contains the mesosiderites main group pallasites and silicates from iiiab irons the angrites may be marginally resolvable from the hed group within each of these groups internal geologic processes give rise to isotopic variations along a slope 1 2 fractionation line as is well known for terrestrial materials variations of 17o from one planet to another are inherited from the inhomogeneities in the solar nebula as illustrated by the isotopic compositions of chondrites and their constituents among the undifferentiated achondrites five isotopic groups are found 1 aubrites 2 winonaites and iab iiicd irons 3 brachinites 4 acapulcoites and lodranites and 5 ureilites the isotopic compositions of aubrites coincide with the earth and moon and also with the enstatite chondrites these bodies apparently were derived from a common reservoir the isotopic composition of which was established at the chondrule scale by nebular processes isotopic similarities between chondrites and achondrites are seen only for the following instances 1 enstatite chondrites and aubrites 2 h chondrites and he irons and 3 l or ll chondrites and iva irons the isotopic data also support the following genetic associations 1 winonaites and iab iiicd irons 2 acapulcoites and lodranites and 3 ureilites and dark inclusions of c3 chondrites an attempt to reconcile the whole planet isotopic compositions of earth mars and the eucrite parent body with mixing models of their chemical compositions failed it is not possible to satisfy both the chemical and isotopic compositions of the terrestrial planets using known primitive solar system components

carbonates in antarctic ordinary chondrites inferred from infrared diffuse reflectance spectra examination of antarctic ordinary chondrites was made through use of infrared diffuse reflectance spectroscopy the spectra of all the antarctic ordinary chondrites measured show weak absorption bands near 1350 cm 1 7 4 m which are caused by carbonates probably hydrated carbonates the band is not present after acid dissolution consistent with the carbonate identification the carbonates were probably produced by terrestrial weathering since the spectra of recently fallen non antarctic chondrites nuevo mercurio h5 and la criolla l6 do not show the 1350 cm 1 7 4 m band infrared diffuse reflectance spectroscopy is useful for easily detecting the presence or absence of the weathering produced carbonates in meteorites

variation in bioturbation with water depth on marine slopes a study on the little bahamas bank abstract reconstructing the paleoceanography of intermediate depth waters is dependent on sedimentary records preserved on marine slopes but knowledge of bioturbation processes in such slope environments is much poorer than for the deep sea in this study 210 pb profiles were measured for the upper 20 cm of sediment from five box cores taken on the slopes of the bahamas in water depths ranging from 400 to 1500 m these were compared with data from the bahamas bank tops and from elsewhere to assess the rate and depth of mixing in the slope environment excess 210 pb inventories are too high to explain by water column decay of 226 ra and are derived largely from atmospheric fallout down core 210 pb xs profiles show an upper zone where 210 pb xs activities decrease exponentially with depth suggesting uniform mixing and a lower zone with patchy 210 pb values reflecting isolated burrows in contrast to bank top sediment which shows 210 pb xs mixing to depths of 40 cm and mixing rates of 1000 cm2 kyr mixing of 210 pb on the slopes penetrates to only 8 cm with mixing rates of 210 pb derived mixing activity in ocean margin sediments diffusive versus nonlocal mixing j mar res 54 1207 1227 a simple model is used to assess the effects of mixing on typical bahamian slope sediments which have deposition rates and compositions which vary dramatically in response to sea level change proxy records such as 18 o are expected to be displaced by up to 0 8 kyr in bulk sediment and individual sediment constituents may be moved by up to 2 kyr relative to one another these mixing effects are reasonably small and may be safely ignored for some studies but for high resolution records or studies where precise age control is important bioturbation of slope sediments should be considered

210 pb and 14 c as indicators of callianassid bioturbation in coral reef sediment abstract callianassid shrimps are the dominant endofauna of reef top sediments on john brewer reef a small platform reef in the central section of australia s great barrier reef province sediment reworking by these shrimps was investigated using the 210pb radioisotope in conjunction with 14c radiometry and textural data 210pb analyses of cores from two reef top sites revealed a classical tripartite subdivision characteristic of depositional settings in which sediment reworking dominates over sediment accumulation 1 a vertical surface mixed layer sml extending to a depth of 50 cm beneath the sediment surface and representing a zone of intensive callianassid reworking 2 an intermediate region of radioa tive attenuation in which excess 210pb activity decreases logarithmically to a depth of slightly more than one meter beneath the sediment surface and interpreted as representing a region utilized less frequently by callianassa for coarse grain storage and predator avoidance 3 a basal region beyond callianassid influence of consistently low background levels of 210pb activity sediment turnover rates in excess of 120 cm2 yr 1 in the sml and up to 32 cm2 yr 1 in the region of radioactive attenuation were high compared to those typical of siliciclastic continental shelf and deep sea deposits emphasizing the intensity of callianassid reworking in shallow coral reef environments 210pb geochronology is unsuitable for determining sediment accumulation rates in such settings because the disruptive impact of callianassa gives rise to unacceptably high figures the depth of callianassid influence established by 210pb radiometry corresponds to points of inflection indicating the bases of vertical surficial sections in 14c subsurface age profiles for the two john brewer reef sites inflection points in other 14c profiles may similarly indicate sediment reworking depths at locations across the reef where 210pb data were not obtained

achondrites and igneous processes on asteroids the possible roles of partial melting and fractional crystallization in the formation of eucrite and ureilite achondrites are discussed summarizing the results of recent petrological investigations and theoretical modeling efforts typical data are presented graphically and it is found that there is as yet no consensus on the correct model of achondrite evolution and hence no agreement on the chemistry of the parent bodies assuming that the ureilites formed as adcumulates their properties support a role for fractionation in relatively small bodies even though the magmatic composition of the ureilite parent bodies is different from that of terrestrial cumulates

origin of polymict breccias on asteroids deduced from their pyroxene fragments cumulate eucrite noncumulate eucrite and diogenite meteorites are considered to have come from the crust of one or similar parent asteroid howardites are regarded as regolith breccias of eucrites and diogenites and polymict eucrites are regarded as polymict breccias of eucrites these polymict breccias show many textural and chemical features in order to gain a better understanding of the origin of polymict breccias and the origin of their components we investigated four polymict breccias yamato y 791439 y 791192 y 82009 and y 82049 with a scanning electron microscope sem equipped with a chemical mapping system and by electron probe microanalysis epma we analyzed all pyroxene grains with chemical maps classified them by chemical composition and observed their chemistry and mineralogy in detail the characteristics of pyroxenes suggest that the polymict breccias were generated by gathering locally ordinary eucrites and cumulate eucrites the chemical evolutionary features of the pyroxenes such as homogenization chemical zoning and exsolution lamellae suggest that there were at least two long annealing events and one short or low temperature annealing event separated by mixing events local heterogeneity on the asteroidal crust is also suggested

differences between antarctic and non antarctic meteorites an assessment abstract the discovery of a statistically significant number of meteorites in antarctica over the past 20 years has posed many questions one of the most intriguing suggestions that came up during the study of the antarctic samples was that there might be a difference between the parent populations of antarctic and non antarctic meteorites this interpretation was put forward after the detection of a significant difference in the abundances of volatile and mobile trace elements in h l and c chondrites and achondrites other major differences include the occurrence of previously rare or unknown meteorites different meteorite type frequencies petrographic characteristics oxygen isotopic compositions and smaller average masses in addition antarctic meteorites have greater terrestrial residence ages and have collected on the ice shield over several 10 5 years the reality of numerous such differences has now been established beyond doubt however the main question regarding the cause of these differences remains it seems that they have a wide variety of origins ranging from pre terrestrial traits to collection recovery effects and terrestrial weathering studies of terrestrial weathering have shown that over the long time the meteorites spend in and on the ice even subtle processes can produce substantial effects for future investigations it will be important to pay more attention to the weathering status of samples and to develop a more reliable and quantitative weathering index e g based on infrared reflectance spectrometry or differential scanning calorimetry not all differences between the antarctic and non antarctic meteorite populations can be explained by weathering pairing or different collection procedures variable trace element abundances and distinct differences in the thermal history and thermoluminescence characteristics have to be interpreted as being pre terrestrial in origin such differences imply the existence of meteoroid streams whose existence poses problems in the framework of our current knowledge of celestial mechanics however several independent studies support the existence of such meteoroid streams thus being consistent with the suggestion of a time variable influx of extraterrestrial material to earth the generally smaller average size of antarctic meteorites may be the cause for the different meteorite type frequency and the higher abundance of rare samples because smaller meteorites may come from a slightly different parent population in this paper we summarize the contributions in this series and provide a review of the current state of the question for the reality and cause of differences between antarctic and non antarctic meteorites

subsolidus ree partitioning between pyroxene and plagioclase in cumulate eucrites an ion microprobe investigation abstract in an attempt to elucidate the relationship between the cumulate eucrites and the noncumulate main series eucrites we have examined the trace element systematics of plagioclase grains that coexist with inverted pigeonites of the cumulate eucrites analyses were done by secondary ion mass spectrometry sims plagioclase compositions are uniform in trace element abundances within grains from each cumulate eucrite but are variable between the four analyzed moama moore county serra de mage and binda shapes of ci normalized trace element abundance patterns of the plagioclase grains of the cumulates are typical of plagioclase showing a lree enriched pattern with positive eu anomalies reflecting the site preference of eu 2 in the feldspar structure using trace element concentrations of the pyroxenes orthopyroxene pigeonite augite pun and papike 1995 and plagioclase this study we calculate the subsolidus partition coefficients ds for the rees and y between plagioclase and pyroxenes in the examined cumulate eucrites trace element systematics suggest that igneous trace element signatures have been altered by subsolidus exchange for both the plagioclase and pyroxene calculated hypothetical parental melt patterns determined from pyroxene and plagioclase are different and can differ by a factor of 4 5 for individual rees

mineralogy of meteorite groups approximately 275 mineral species have been identified in meteorites reflecting diverse redox environments and in some cases unusual nebular formation conditions anhydrous ordinary carbonaceous and r chondrites contain major olivine pyroxene and plagioclase major opaque phases include metallic fe ni troilite and chromite primitive achondrites are mineralogically similar the highly reduced enstatite chondrites and achondrites contain major enstatite plagioclase free silica and kamacite as well as nitrides a silicide and ca mg mn na cr k and ti rich sulfides aqueously altered carbonaceous chondrites contain major amounts of hydrous phyllosilicates complex organic compounds magnetite various sulfates and sulfides and carbonates in addition to kamacite and taenite iron meteorites contain carbides elemental c nitrides phosphates phosphides chromite and sulfides silicate inclusions in iab iiicd and iie iron meteorites consist of mafic silicates plagioclase and various sulfides oxides and phosphates eucrites howardites and diogenites have basaltic to orthopyroxenitic compositions and consist of major pyroxene and calcic plagioclase and several accessory oxides ureilites are made up mainly of calcic chromian olivine and low ca clinopyroxene embedded in a carbonaceous matrix accessory phases include the c polymorphs graphite diamond lonsdaleite and chaoite as well as metallic fe ni troilite and halides angrites are achondrites rich in fassaitic pyroxene i e al ti diopside minor olivine with included magnesian kirschsteinite is also present martian meteorites comprise basalts lherzolites a dunite and an orthopyroxenite major phases include various pyroxenes and olivine minor to accessory phases include various sulfides magnetite chromite and ca phosphates lunar meteorites comprise mare basalts with major augite and calcic plagioclase and anorthositic breccias with major calcic plagioclase several meteoritic phases were formed by shock metamorphism martensite 2 fe ni has a distorted body centered cubic structure and formed by a shear transformation from taenite during shock reheating and rapid cooling the c polymorphs diamond lonsdaleite and chaoite formed by shock from graphite suessite formed in the north haig ureilite by reduction of fe and si possibly from olivine via reaction with carbonaceous matrix material ringwoodite the spinel form of mg fe 2sio4 and majorite a polymorph of mg fe sio3 with the garnet structure formed inside shock veins in highly shocked ordinary chondrites secondary minerals in meteorite finds that formed during terrestrial weathering include oxides and hydroxides formed directly from metallic fe ni by oxidation phosphates formed by the alteration of schreibersite and sulfates formed by alteration of troilite

spatially quantitative seafloor habitat mapping example from the northern south carolina inner continental shelf abstract naturally occurring hard bottom areas provide the geological substrate that can support diverse assemblages of sessile benthic organisms which in turn attract many reef dwelling fish species alternatively defining the location and extent of bottom sand bodies is relevant for potential nourishment projects as well as to ensure that transient sediment does not affect reef habitats particularly in sediment starved continental margins furthermore defining sediment transport pathways documents the effects these mobile bedforms have on proximal reef habitats thematic mapping of these substrates is therefore crucial in safeguarding critical habitats and offshore resources of coastal nations this study presents the results of a spatially quantitative mapping approach based on classification of sidescan sonar imagery by using bottom video for image to ground control digital image textural features for pattern recognition and an artificial neural network for rapid quantitative multivariable decision making this approach resulted in recognition rates of hard bottom as high as 87 the recognition of sand bottom was less successful 31 this approach was applied to a large 686 km2 high quality 2 m resolution sidescan sonar mosaic of the northern south carolina inner continental shelf results of this analysis indicate that both surficial sand and hard bottoms of variable extent are present over the study area in total 59 of the imaged area was covered by hard bottom while 41 was covered by sand qualitative spatial correlation between bottom type and bathymetry appears possible from comparison of our interpretive map and available bathymetry hard bottom areas tend to be located on flat low lying areas and sandy bottoms tend to reside on areas of positive relief published bio erosion rates were used to calculate the potential sediment input from the mapped hard bottom areas rendering sediment volumes that may be as high as 0 8 million m3 yr for this portion of the south carolina coast

differentiation history of the mesosiderite parent body constraints from trace elements and manganese chromium isotope systematics in vaca muerta silicate clasts abstract we report here the results of a study of trace element microdistributions and 53mn 53cr systematics in several basaltic and orthopyroxenitic clasts from the vaca muerta mesosiderite ion microprobe analyses of selected trace and minor element abundances in minerals of the silicate clasts indicate that following igneous crystallization these clasts underwent extensive metamorphic equilibration that resulted in intra and inter grain redistribution of elements there is also evidence in the elemental microdistributions that these clasts were subsequently affected to varying degrees by alteration resulting from redox reactions involving the indigenous silicates and externally derived reducing agents such as phosphorus derived from the mesosiderite metal at the time of metal silicate mixing furthermore our results suggest that the varying degrees of alteration by redox reactions recorded in the different clasts were most likely facilitated by different degrees of remelting induced by heating during the metal silicate mixing event after taking into account the effects of these postmagmatic secondary processes comparison of the trace and minor element concentrations and distributions in minerals of basaltic and orthopyroxenitic clasts with those of noncumulate eucrites and diogenites respectively suggests that the primary igneous petrogenesis including parent magma and source compositions of vaca muerta silicates were similar to those of achondritic meteorites of the howardite eucrite diogenite hed association internal 53mn 53cr isochrons obtained for two basaltic pebble 16 and 4679 and two orthopyroxenitic 4659 and 4670 clasts show that chromium isotopes are equilibrated within each clast nevertheless just as for noncumulate eucrites and diogenites 53cr excesses in whole rock samples of the basaltic clasts 1 01 e in pebble 16 1 07 e in 4679 are significantly higher than in the orthopyroxene rich clasts 0 62 e in 4659 0 53 e in 4670 as in the case of the hed parent body this suggests that mn cr fractionation in the parent body of the vaca muerta silicate clasts occurred very early in the history of the solar system when 53mn was still extant however the slope of the 53mn 53cr isochron defined by the whole rock samples of vaca muerta clasts corresponding to a 53mn 55mn ratio of 3 3 0 6 10 6 is distinctly lower than that defined by the hed whole rock samples corresponding to a 53mn 55mn ratio of 4 7 0 5 10 6 indicating that the global mn cr fractionation event that established mantle source reservoirs on the parent body of the vaca muerta silicate clasts occurred 2 ma after a similar event on the hed parent body

provenance discrimination of the clay sediment in the western taiwan strait and its implication for coastal current variability during the late holocene this study aims to quantify the contribution of yangtze clays to the sediment accumulation in the western taiwan strait and reconstruct the strength of chinese coastal current ccc since middle ho

stable isotopes and the noncarbonaceous derivation of ureilites in common with nearly all differentiated planetary materials abstract the abundant diverse ureilite meteorites are peridotitic asteroidal mantle restites that have remarkably high bulk carbon contents average 3 wt and have long been linked to the so called carbonaceous chondrites although this term is potentially misleading because the high petrologic type carbonaceous chondrites are if anything c poor compared to ordinary chondrites ureilite oxygen isotopic compositions i e diversely negative ccam like 17o viewed in isolation have long been viewed as confirming the carbonaceous chondritic derivation hypothesis however a very different picture emerges through analysis of a compilation of recently published high precision isotopic data for chromium titanium and nickel for ureilites and various other planetary materials ureilites have lower e62ni and far lower e50ti and e54cr than any known variety of carbonaceous chondrite on a plot of e50ti vs e54cr and similarly 17o vs e54cr ureilite compositions cluster far from and in a direction approximately orthogonal to a trend internal to the carbonaceous chondrites and the carbonaceous chondrites are separated by a wide margin from all other planetary materials i conclude that notwithstanding the impressive resemblance to carbonaceous chondrites in terms of diversely negative 17o the ureilite precursors accreted from preponderantly noncarbonaceous sensu stricto materials despite total depletion of basaltic matter the ureilites retain moderate pyroxene olivine ratios which is an expected outcome from simple partial melting of moderate sio2 feo mgo noncarbonaceous chondritic material but would imply an additional process of major reduction of feo if the precursor material were carbonaceous chondritic the striking bimodality of planetary materials on the e50ti vs e54cr and 17o vs e54cr diagrams may be an extreme manifestation of the effects of episodic accretion of early solids in the protoplanetary nebula however an alternative admittedly speculative explanation is that the bimodality corresponds to a division between materials that originally accreted in the outer solar system carbonaceous and materials that accreted in the inner solar system noncarbonaceous including the ureilites

classification of mafic clasts from mesosiderites implications for endogenous igneous processes we have analyzed thirteen igneous pebbles from the vaca muerta eet87500 and bondoc mesosiderites by electron microprobe and instrumental neutron activation and combined these data with literature data for forty three analyzed mesosiderite clasts we classify these well characterized clasts into the following five principal groups 1 1 polygenic and monogenic cumulates 39 are coarse grained gabbros that are highly depleted in incompatible elements relative to h chondrites they formed at moderate depth either as residues of low degree partial melting of pre existing cumulate eucrites or as cumulates from parent melts similar to cumulate eucrites 2 2 polygenic basalts 30 are finer grained rocks with positive europium anomalies la lu ratios 1 and lower rare earth element abundances than basaltic eucrites it seems likely that these rocks were formed near their parent body surface by remelting mixtures of major amounts of basaltic eucrites and lesser amounts of cumulate eucrites 3 3 quench textured rocks comprise two compositional groups a those which resemble basaltic eucrites 5 and b those which resemble cumulate eucrites 2 the quench textured rocks are probably monogenic they formed most likely when small scale impacts at their parent body surface totally melted small amounts of basaltic or cumulate eucrite material 4 4 monogenic basalts 11 resemble basaltic eucrites and formed by endogenous igneous processes on the mesosiderite parent body mpb the monogenic basalts and those quench textured rocks that resemble basaltic eucrites in composition plot subparallel to the nuevo laredo trend eucrites on diagrams of incompatible element concentration vs mg previous work has shown that the nuevo laredo trend eucrites were probably produced by fractional crystallization it seems likely that the monogenic basalts from the mpb had a similar origin 5 5 ultramafic rocks are cumulates consisting mainly of large crystals of orthopyroxene 9 or olivine 4 orthopyroxenite clasts closely resemble diogenites and were formed most likely by endogenous igneous processes olivine crystals vary significantly in major element composition some may be endogenous but others may have been derived from the disrupted mantle of a different parent body

the parent magmas of the cumulate eucrites a mass balance approach the cumulate eucrite meteorites are gabbros that are related to the eucrite basalt meteorites the eucrite basalts are relatively primitive nearly flat ree patterns with la approx 8 30 x ci but the parent magmas of the cumulate eucrites have been inferred as extremely evolved la to greater than 100 x ci this inference has been based on mineral magma partitioning and on mass balance considering the cumulate eucrites as adcumulates of plagioclase pigeonite only both approaches have been criticized as inappropriate here mass balance including magma equilibrium pigeonite equilibrium plagiociase is used to test a simple model for the cumulate eucrites that they formed from known eucritic magma types that they consisted only of magma crystals in chemical equilibrium with the magma and that they were closed to chemical exchange after the accumulation of crystals this model is tested for major and rare earth elements ree the cumulate eucrites serra de mage and moore county are consistent in both ree and major elements with formation by this simple model from a eucrite magma with a composition similar to the nuevo laredo meteorite serra de mage as 14 magma 47 5 pigeonite and 38 5 plagioclase moore county as 35 magma 37 5 pigeonite and 27 5 plagioclase these results are insensitive to the choice of mineral magma partition coefficients results for the moama cumulate eucrite are strongly dependent on choice of partition coefficients for one reasonable choice moama s composition can be modeled as 4 nuevo laredo magma 60 pigeonite and 36 plagioclase selection of parent magma composition relies heavily on major elements the ree cannot uniquely indicate a parent magma among the eucrite basalts the major element composition of y 791195 can be fit adequately as a simple cumulate from any basaltic eucrite composition however y 791195 has lree abundances and la lu too low to be accommodated within the model using any basaltic eucrite composition and any reasonable partition coefficients postcumulus loss of incompatible elements seems possible it is intriguing that serra de mage moore county and moama are consistent with the same parental magma could they be from the same igneous body on the eucrite parent asteroid 4 vesta

flexural isostasy constraints from gravity and topography power spectra we have used spherical harmonic coefficients that describe earth s gravity anomaly and topography fields to quantify the role of isostasy in contributing to crustal and upper mantle structure power spectra reveal that the gravity effect of topography and its flexural compensation contributes significantly to the observed free air gravity anomaly spectra for spherical harmonic degree 33 400 and lower n 33 degrees but topography appears either uncompensated or fully compensated at these degrees irrespective of the actual te all isostatic models underpredict the spectra at 2 n 12 and so we interpret the low order earth s gravity field as caused at least in part by non isostatic processes due to dynamic motions such as those associated with convective upwellings and downwellings in earth s mantle

petrogenesis of d orbigny like angrite meteorites and the role of spinel in the angrite source this research was supported by an australian national university phd scholarship to smck who is currently a postdoctoral fellow of the research foundation flanders

mud capped dredge pits an experiment of opportunity for characterizing cohesive sediment transport and slope stability in the northern gulf of mexico abstract mud capped dredge pits mcdps defined as sand borrow sites from paleo river channels with cohesive sediment capped walls are used for northern gulf of mexico ngom coastal restoration projects due to lower cost than more distal restoration resources mcdp evolution including infilling and pit wall slope stability is poorly understood in relation to sandy borrow areas we present and interpret bathymetric data from sandy point mcdp which was constructed in 2012 about 20 km northwest of southwest pass the most active mississippi river distributary in water depths of 11 m repeat bathymetric surveys show the pit is infilling 54 cm or volumetrically 200 000 m3 per year which is on the same order as seasonal scale and an order of magnitude higher than the decadal scale vertical accretion rates observed seaward of southwest pass this infilling rate is higher than predicted based solely on excavated volume when compared with other dredge pits in sandy substrate sediment starved settings mcdp infill is volumetrically dominated by far field here defined as river plume or shelf bed resuspension sediment with only 9 of pit infill from pit wall failure geomorphic comparison of sandy point mcdp walls with southwest pass mudflow gully walls shows that the mcdp is oversteepened relative to natural depression features in this setting the convergence of mcdp and mudflow gully gradients towards a common value 4 5 may represent an angle of repose in lieu of decadal scale forcings findings from this experiment of opportunity show that mcdps 1 are effective sediment traps 2 have steep but relatively laterally stable walls 3 do not represent significant risk to infrastructure in a 3 year time scale and 4 are predicted to infill within about 2 decades provided a proximal sediment source exists

two new eucrite breccias from northwest africa this work describes two newly discovered eucrite breccias three presumably paired meteorites all named northwest africa nwa 6105 and nwa 6106 for each meteorite major and minor element compositions of minerals were determined using the electron microprobe pyroxene fe mn co variations and bulk rock oxygen isotope compositions confirm their classification as eucrites variations in mineral compositions and textures are attributed to differences in clast types present i e basaltic or cumulate eucrite the pyroxene compositions support the hypothesis that samples nwa 6105 1 6105 2 and 6105 3 are paired polymict eucritic breccias whereas sample nwa 6106 is a monomict basaltic eucritic breccia two pyroxene geothermometry yields temperatures too low for igneous crystallization the variation in temperatures among samples suggests that metamorphism occurred prior to brecciation

an anomalous eucrite dhofar 007 and a possible genetic relationship with mesosiderites we studied the texture mineralogy and bulk chemical composition of dhofar 007 a basaltic achondrite dhofar 007 is a polymict breccia that is mostly composed of coarse grained granular cg clasts with a minor amount of xenolithic components such as a fragment of mg rich pyroxene the coarse grained relict gabbroic texture mineral chemistry and bulk chemical data of the coarse grained clast indicate that the cg clasts were originally a cumulate rock crystallized in a crust of the parent body however in contrast to monomict eucrites the siderophile elements are highly enriched and could have been introduced by impact events dhofar 007 appears to have experienced a two stage postcrystallization thermal history rapid cooling at high temperatures and slow cooling at lower temperatures the presence of pigeonite with closely spaced fine augite lamellae suggests that this rock was cooled rapidly from higher temperatures 0 5 c yr at 1000 c than typical cumulate eucrites however the presence of the cloudy zone in taenite and the ni profile across the kamacite taenite boundaries indicates that the cooling rate was very slow at lower temperatures 1 10 c myr at 600 700 c the slow cooling rate is comparable to those in mesosiderites and pallasites the two stage thermal history and the relative abundance of siderophile elements similar to those for metallic portions in mesosiderites suggest that dhofar 007 is a large inclusion of mesosiderite however we cannot rule out a possibility that dhofar 007 is an anomalous eucrite

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

siderophile and other geochemical constraints on mixing relationships among hed meteoritic breccias we have used neutron activation and electron probe fused bead techniques to analyze the bulk major and trace element compositions of 104 named hed meteorites about 100 102 distinct meteorites depending upon pairings including 32 polymict eucrites 30 howardites and six diogenites most were not previously analyzed for siderophile trace elements many not even for major elements our typical sample was 350 mg and in some cases two separate chips were analyzed as a test of meteorite heterogeneity meteorites with extraordinary compositions include bluewing 001 an unequilibrated eucrite that is rich in ti sm and other incompatible elements y 791192 a cumulate dominated polymict eucrite and lew 87002 an oddly sm rich howardite dominated by a ferroan variety of diogenite the eucrite diogenite mixing ratio is the single most important factor determining the compositions of polymict heds but wide ranges in eucrite incompatible element contents in diogenite cr and v contents and in sc contents of both eucrites and diogenites make for diversity among the polymict heds as our new siderophile data help to show the common practice of describing the entire class of howardites as regolith breccias is erroneous most howardites are fragmental breccias showing no sign of origin from true in the lunar sense i e soil like near surface regolith howardites are highly diverse in ni content often remarkably ni poor compared to lunar regolith breccias however the few 8 howardites with between 300 and 1200 lg g ni consistently show some combination of other traits suggestive of regolith origin most importantly all four cases or five if we include malvern which appears to have been altered by annealing of howardites known to have enrichments in solar wind noble gases belong to the 300 lg g ni group in many cases an abundance of glasses particularly in spheroidal or turbid brown form provides additional evidence for regolith origin we propose that the important subset of howardites that are regolith breccias be formally distinguished by the designation regolithic howardite apart from high siderophile levels the regolithic howardites are compositionally distinctive in having al2o3 consistently near 8 9 wt corresponding to a eucrite diogenite mixing ratio of precisely 2 1 assuming the heds are reasonably representative of the ancient i e pre vestoid launch surface of vesta this clustering of regolith composition is difficult to explain unless most of the ancient diogenite component was brought to the surface in a single early episode i e probably a single great impact after which smaller scale cratering with no further major excavations of diogenite until the vestoid forming event efficiently homogenized the surface such a single excavation model may also help to explain why diogenites in marked contrast with eucrites are seldom polymict and why al2o3 poor diogenite dominated howardites consistently lack major siderophile enrichments the low siderophile contents of polymict eucrites are most enigmatic possibly in the hedasteroidal context low collision velocities etc only materials blended by multiple impacts consistently acquire major enrichments in siderophile elements 2009 elsevier ltd all rights reserved

experimental evidence of fast transport of trace elements in planetary basaltic crusts by high temperature metamorphism incompatible elements ies such as k p ti and rare earth elements rees provide important constraints on the geochemistry and chronology of basaltic meteorites most of which experienced complicated post crystallization histories these elements are immobile under subsolidus conditions because of their slow diffusion rates in planetary basalt minerals such as pyroxene and plagioclase thus ies are considered to preserve in most cases reliable records of formation processes even in ancient rocks that have undergone moderate thermal processing however observations of natural planetary samples suggest that melting of ie accessory carrier phases enhances the mobilization of such elements here we show that ies are rapidly transported by near solidus partial melting of highly ie enriched minor phases including ca phosphate and ti rich phases these partial melts occur as interconnected veins along cracks and fractures and as thin films on surfaces of pore spaces indicating that the melt mobilization is driven by surface tension the melt transport provides the necessary condition for melt migration consistent with the presence of the depleted basaltic eucrites also reaction between major minerals pyroxene and plagioclase and partial melts may cause disturbance and resetting of some isotopic systems these results have important implications for a range of geochemical investigations in particular the elemental fractionation resulting from such partial melting may result in improper age determinations

hurricane associated ebb tidal delta sediment dynamics bathymetric surveys conducted before and after the 2005 hurricane season at little pass timbalier in the mississippi river delta plain united states demonstrate that 9 1 2 4 10 6 m 3 of sediment was eroded from a 47 9 km 2 area between the two surveys hurricanes cindy katrina and rita passed within 300 km of the tidal inlet comparison of before and after bathymetric data sets shows that the distal portion of the ebb tidal delta etd was the site of 63 of the total erosion locally resulting in 400 m of shoreface retreat shoaling 0 75 1 0 m in the seawardmost portion of the ebb channel and erosion in the landward portion 1 5 m resulted in a 160 m landward shift of the inlet throat collectively these processes forced the landward migration of the entire tidal inlet and etd system there has been considerable discussion about large volumes of mineral sediment deposited on the mississippi river delta plain interior marsh surface as a result of hurricanes however the origin of this sediment is unknown we identify the distal portion of an etd as one possible sediment source and hypothesize that etd and shoreface sediment is mobilized by hurricane waves and transported landward by surge induced currents our results emphasize the role of frequent and intense hurricanes in long term coastal evolution and as a mechanism for regional sediment retention within the transgressive system beyond typical barrier overwash processes

a model composition of the basaltic achondrite planetoid the basaltic achondrites eucrites diogenites and howardites have compositions on a common oxygen isotope mass fractionation line and probably formed from a chondritic precursor also lying on that same line no chondritic meteorite group has the same isotopic signature as the basaltic achondrites so the oxygen isotope ratios of several known chondritic groups were used to construct a two component mixing model for the composition of the precursor this model does not provide a unique solution as several mixtures of ordinary and carbonaceous precursors will satisfy the isotopic constraints the fe mn mg abundances of the precursors and of the eucrites were used to provide an additional constraint the precursor composition selected for study is a mixture of 70 wt h chondrite with 30 wt cm chondrtte this mixture generates a slightly feo rich silicate precursor that after reduction and separation of an iron sulfide core is compatible with the mantle of the basaltic achondrite planetoid bap having a similar composition to that modeled by dreibus and wanke 1980 partial melting experiments of this h cm precursor composition suggest that eucritic magmas could be formed in such a mantle these experiments also suggest that the mantle must have experienced metal loss to constrain the fe mn ratios and probably significant olivine fractionation as well diogenite precursors may also be generated in this mantle composition as feo reduction and olivine fractionation lead to the formation of sio2 enriched compositions from which diogenite source magmas may be extracted if mixing of material from two very distinct chondritic reservoirs h and cm chondrites is realistic then an asteroid scale mixing process is needed to generate the achondrite precursor large impact events would provide a plausible method for mixing material from reservoirs with quite different oxygen isotope characteristics to assemble the basaltic achondrite planetoid

mesosiderite clasts with the most extreme positive europium anomalies among solar system rocks pigeonite plagioclase gabbros that occur as clasts in mesosiderites brecciated stony iron meteorites show extreme fractionations of the rare earth elements rees with larger positive europium anomalies than any previously known for igneous rocks from the earth moon or meteorite parent bodies and greater depletions of light rees relative to heavy rees than known for comparable cumulate gabbros the ree pattern for merrillite in one of these clasts is depleted in light rees and has a large positive europium anomaly as a result of metamorphic equilibration with the silicates the extreme ree ratios exhibited by the mesosiderite clasts demonstrate that multistage igneous processes must have occurred on some asteroids in the early solar system melting of the crust by large scale impacts or electrical induction from an early t tauri phase sun may be responsible for these processes

l olivine dans les howardites origine et implications pour le corps parent de ces meteorites achondritiques abstract electron microprobe analyses have been performed on 300 olivine grains found in 11 howardites the olivine compositions almost continuously range from fa 8 to fa 89 with two prominent populations at fa 13 and fa 30 the tail of the fayalite contents distribution may correspond to the succession of several small clusters of fe rich olivine grains most howardites have olivine populations in common that would result from the fragmentation of different rocks of the howardites parent body the distribution of the olivine grains between several groups of different feo mno ratios indicates olivine crystallization from distinct magmas the chemical characteristics of the olivines of the pallasites diogenites and mesosiderites are found among the olivines of the howardites and suggests a common parent body for these different types of meteorites the differentiation model of the eucrites parent body proposed by stolper 1977 is extended to the partial fusion of distinct assemblages silicates metal which could proceed from recrystallizations under different oxidation reduction conditions of a primordial chondritic material depleted in volatile elements

update on terrestrial ages of antarctic meteorites abstract cosmic ray produced 36 cl half life 3 01 10 5 years has been measured in 90 antarctic meteorites by accelerator mass spectrometry the terrestrial ages of the meteorites were calculated from the results after excluding possible paired objects 138 terrestrial ages from 18 different locations are available from 14 c 81 kr and 36 cl measurements for application to antarctic meteorite and glaciological studies the terrestrial ages of allan hills meteorites vary from 2000 years to 1 million years and are clearly longer than those of yamato meteorites and other antarctic meteorites the oldest allan hills meteorites were found close to the eastern edge and in the southeast of the main icefield among all antarctic meteorites measured to date only l and ll chondrites have terrestrial ages older than 370 000 years

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

geoacoustic inversion for the seabed transition layer using a bernstein polynomial model this paper develops an inversion method for the seabed transition layer at the water sediment interface often found in muddy sediments which provides density and sound speed profiles that were previously not resolvable the resolution improvements are achieved by introducing a parametrization that captures general depth dependent gradients in geoacoustic parameters with a small number of parameters in particular the gradients are represented by a sum of bernstein basis functions weighted by unknown coefficients compared to previous forms found in the literature the bernstein based parametrization can represent a wider range of depth dependent geoacoustic profiles using fewer parameters which leads to reduced uncertainty and improved resolution in addition the bernstein basis is the most stable polynomial representation in that small perturbations to the unknown coefficients result in small localized perturbations to the geoacoustic profile thereby providing an efficient exploration of the parameter space using markov chain methods in nonlinear inversion geoacoustic profiles at four mud sites on the malta plateau are studied with the proposed approach results show exceptional resolution of density profiles estimated with low uncertainty and clear sensitivity to sediment features of centimeter scale

chemical composition of the howardite parent body deduced from kapoeta primary mafic magmas chemical data are presented for three mafic clasts extracted from the kapoeta howardite bulk compositions and petrologic observations suggest that two of these lithic clasts represent olivine plagioclase bearing orthopyroxenites chondrite relative refractory lil abundances of two of the clasts are inferred to represent primary mg rich magmas produced by extensive 70 partial melting of a source composition indistinguishable from the silicate fraction of average ch cl ordinary chondrites with the exception of the depletion of the alkalis na and k by a factor of 13 1 in the source composition a metal free and volatile depleted kapoeta parent body kpb is subsequently deduced and is shown to compare very well with other similarly derived achondrite parent body apb and howardite parent body hpb estimates but not to parent body estimates derived from inferences based on eucrite phase equilibrium studies other implications suggest that the kpb is heterogeneous with respect to fe mg ratios

lithium systematics in howardite eucrite diogenite meteorites implications for crust mantle evolution of planetary embryos we present lithium li abundances and isotope compositions in a suite of howardites eucrites and diogenites heds these meteorites most likely originated from asteroid vesta and were delivered to earth by a series of independent impact events the li concentrations show striking differences between li poor diogenites plus cumulate eucrites and li enriched eucrites whilst howardites have li abundances intermediate between eucrites and diogenites contrary to li elemental inter group differences li isotope compositions are irresolvable among these individual groups of hed meteorites despite their wildly distinct petrography attesting to insignificant li isotope fractionation during formation of a thick basaltic crust by melting of the vestan mantle the mean li isotope composition of bulk silicate vesta is estimated at 3 7 0 6 1 intermediate to that of the earth versus mars and moon but identical with these terrestrial bodies within uncertainty this further validates largely homogeneous inner solar system solids from the li isotope perspective and supports the lack of loss of moderately volatile elements from planetary embryos during their magmatic histories because li does not follow depletion trends inferred from more volatile elements pasamonte eucrite has the same li isotope composition as other eucrites although it may not be directly linked to vesta these observations are also important for generating li elemental and isotope signatures in juvenile basaltic crusts of large terrestrial planets and numerous planetary embryos in the early solar system a combination of cv l chondrites may be less suitable for building vesta from li perspective but this may face sampling bias of available data and only further analyses may resolve this issue alternatively significant shift of 1 towards heavier li isotope compositions must have occurred during thermal processing of cv l 2 2 2 8 mixture in order to account for the observed li isotope systematics in hed meteorites no correlation is observed between li versus zn fe or si isotopes respectively implying unrelated processes of forming stable isotope variations observed in hed meteorites

olivine coronas metamorphism and the thermal history of the morristown and emery mesosiderites abstract coronas are present on all millimeter sized mineral clasts of olivine in the emery and morristown mesosiderites and are a manifestation of high temperature t 850 1100 c metamorphism these coronas formed by reaction and diffusion between olivine and a mesosiderite like matrix assemblage the bulk composition of the coronas can be approximated by a mixture of 10 25 wt olivine and as 90 75 wt metal free matrix except for p and cr which are significantly enriched in coronas phosphorus and cr diffused relatively rapidly to coronas and were derived from a large volume of matrix most likely from metal that was originally enriched in these elements prior to metamorphism the coronas in both meteorites show a similar zone sequence but are systematically thicker in emery 800 m wide than in morristown 350 m wide suggesting that emery experienced more grain growth and more intensive metamorphism than morristown textural relationships suggest that corona formation and high temperature metamorphism occurred largely after intensive millimeter scale brecciation and after or during metal silicate mixing a local equilibrium model can explain many features of the coronas but chemical equilibrium was maintained only on a very small scale overgrowths are present on plagioclase in the coronas of both mesosiderites and probably formed during high temperature metamorphism the compositional interface between core and overgrowth plagioclase is extremely sharp suggesting that cooling rates were 0 1 c y at the peak temperature of metamorphism consistent with high temperature metamorphism occurring in a near surface region of the parent body

al sm eu sr systematics of eucrites and moon rocks implications for planetary bulk compositions abstract analysis of the eu and sr anomalies of eucrites and lunar rocks allows constraints to be placed on the bulk compositions of the eucrite parent body epb and the moon the elements al ree and sr all are essentially incompatible with the major minerals of these small low o 2 bodies except for plagioclase into which al sr and eu tend to concentrate therefore the hypothesis that al ree and sr in the epb and the moon are all in proportions close to those in the bulk solar system i e chondrites leads to certain predictions about the concentrations of these elements in samples affected by plagioclase fractionation the predictions are almost ideally fulfilled by eucrites and lunar samples for the epb the ratios ree al sr al and sr ree are constrained to be probably within 10 almost certainly within 20 of the chondritic ratios for the more complicated moon the constraints are less precise ree al is very probably within 25 of chondritic sr al and sr ree are probably within 35 of chondritic these findings are proof that there is a strong similarity between the bulk compositions of the planets and the compositions of chondritic meteorites the eucrites sm eu sr systematics are also valuable sources of constraints on the distribution coefficients for eu and sr into plagioclase at low o 2 from the slope of data for noncumulate eucrites on a eu sm plot d eu pl liq can be inferred to be 1 1 0 1 0 2 from the slope on a sr sm plot d sr pl liq can be inferred to be 1 5 0 3 in the case of d eu this is in excellent agreement with experimental data in the case of d sr the empirical result is probably more appropriate for eucritic systems than most experimental data which due to compositional effects scatter widely

high calcium pyroxene as an indicator of igneous differentiation in asteroids and meteorites our analyses of high quality spectra of several s type asteroids 17 thetis 847 agnia 808 merxia and members of the agnia and merxia families reveal that they include both low and highcalcium pyroxene with minor amounts of olivine 0 4 high calcium pyroxene is a spectrally detectable and petrologically important indicator of igneous history and may prove critical in future studies aimed at understanding the history of asteroidal bodies the silicate mineralogy inferred for thetis and the merxia and agnia family members requires that these asteroids experienced igneous differentiation producing broadly basaltic surface lithologies together with 4 vesta and its smaller vestoid family members and the main belt asteroid 1489 magnya these new asteroids provide strong evidence for igneous differentiation of at least five asteroid parent bodies based on this analysis of a small subset of the near infrared asteroid spectra taken to date with spex at the nasa irtf we expect that the number of known differentiated asteroids will increase consistent with the large number of parent bodies inferred from studies of iron meteorites

thermal annealing of experimentally shocked feldspar crystals single crystals of sanidine orthoclase microcline oligoclase and labradorite as well as polycrystalline bytownite were shocked experimentally to peak pressures as high as 45 gpa and subsequently annealed under dry conditions for various times at 800 c 900 c and 1000 c these experiments reveal that alkali feldspars do not change their al si distribution due to shock alone but when subjected to shock pressures 22 gpa and then annealed microcline and orthoclase rapidly transform to sanidine displaying a highly disordered al si distribution high diffusivity of k na and ca was observed in a labradorite sample shocked to 26 gpa subsequent annealing may thus disturb chemical structural and isotopic characteristics of shocked minerals and rocks more easily than of unshocked specimens this is of considerable importance for the interpretation of isotopic age data of impact breccias recrystallization textures of annealed diaplectic plagioclase glasses are very distinctive and may be used as a relative measure of the shock pressure experienced by the samples

relative chronology of crust formation on asteroid vesta insights from the geochemistry of diogenites abstract the eucrites and diogenites are meteorites that probably originate from asteroid 4 vesta the upper part of the crust of this body is certainly composed of eucrites which are basaltic or gabbroic rocks diogenites are ultramafic cumulates whose relationships with eucritic lithologies are unknown here we show that the orthopyroxenes of some diogenites display very deep negative eu anomalies eu eu close to 0 1 or lower the contamination of the parental magmas of diogenites by melts derived by partial melting of the eucritic crust can satisfactorily explain the range of the eu anomalies displayed by diogenites thus these anomalies are the first firm indication that parental melts of diogenites have intruded the eucritic crust and consequently are younger than eucrites

quantifying noble gas contamination during terrestrial alteration in martian meteorites from antarctica we investigated exterior and interior subsamples from the martian shergottite meteorites allan hills alh a77005 and roberts massif rbt 04261 for secondary minerals oxygen isotopes ar ar and noble gas signatures electron microprobe investigations revealed that rbt 04261 does not contain any visible alteration even in its most exterior fractures whereas fracture fillings in alha77005 penetrate into the meteorite up to 300 m beyond which the fractures are devoid of secondary minerals light noble gases seem to be almost unaffected by terrestrially induced alteration in both meteorites thus a shock metamorphic overprint of 30 35 gpa can be deduced from the helium measurements in rbt 04261 oxygen isotopes also seem unaffected by terrestrially weathering and variations can easily be reconciled with the differences in modal mineralogy of the exterior and interior subsamples the measurements on irradiated samples ar ar showed a clear martian atmospheric contribution in alha77005 but this is less apparent in our sample of rbt 04261 exterior and interior subsamples show slight differences in apparent ages but the overall results are very similar between the two in contrast krypton and xenon are severely affected by terrestrial contamination demonstrating the ubiquitous presence of elementally fractionated air in rbt 04261 although seemingly contradictory our results indicate that rbt 04261 was more affected by contamination than alha77005 we conclude that irrespective of on which planet the alteration occurred exposure of martian rocks to atmosphere or brine introduces noble gases with signatures elementally fractionated relative to the respective atmospheric composition into the rock and relationships of that process with oxygen isotopes or mineralogical observations are not straightforward

36cl and53mn in antarctic meteorites and10be 36cl dating of antarctic ice cosmic ray produced53mn t1 2 3 7 106years has been measured in twenty antarctic meteorites by neutron activation analysis 36cl t1 2 3 0 105years has been measured in fourteen of these objects by tandem accelerator mass spectrometry cosmic ray exposure ages and terrestrial ages of the meteorites are calculated from these results and from rare gases 14c t1 2 5740years and26al t1 2 7 2 105years data the terrestrial ages range from 3 104 to 5 105 years many of the l3 allan hills chrondrites seem to be a single fall based on these results in addition 10be t1 2 1 6 106years and36cl have been measured in six antarctic ice samples the first measurements of10be 36cl ratios in the ice core samples demonstrate a new dating method for ice

ubiquitous brecciation after metamorphism in equilibrated ordinary chondrites our petrographic study of 42 h and l chondrites of types 4 6 revealed 8 that contain rare chondrules or clasts with olivines and pyroxenes having aberrant fe fe mg ratios for example a chondrule in slovak h5 contains olivine with fa 17 22 elsewhere olivine contains fa 17 18 although these chondrites are not obviously brecciated their ingredients could not have experienced the same degree of metamorphism these rocks must be fragmental breccias that were lithified after peak metamorphism regolith breccias and postmetamorphic fragmental breccias both polymict and monomict may constitute a majority of ordinary chondrites comparison of chondritic and achondritic breccias indicates that chondritic fragmental breccias are often very difficult to recognize because they resemble the fine grained mixtures of chondrules and mineral and chondrule fragments from which they formed in addition the chemical and textural uniformity throughout most of the ordinary chondrite bodies ensures that mixtures of materials from different regions are well disguised contrary to the authors claim the van schmus wood classification of ordinary chondrites does not identify rocks with similar thermal histories the petrologic type of a chondrite is only a measure of the average degree of metamorphism experienced by its ingredients thus attempts to correlate physical properties with petrologic types must fail unless breccia and shock properties are considered the extent of brecciation in ordinary chondrites and most achondrites indicates that meter sized unbrecciated rocks must be rare on the surfaces of their parent bodies

mesosiderite formation on asteroid 4 vesta by a hit and run collision collision and disruption processes of protoplanetary bodies in the early solar system are key to understanding the genesis of diverse types of main belt asteroids mesosiderites are stony iron meteorites that formed by the mixing of howardite eucrite diogenite like crust and molten core materials and provide unique insights into the catastrophic break up of differentiated asteroids however the enigmatic formation process and the poorly constrained timing of metal silicate mixing complicate the assignment to potential parent bodies here we report the high precision uranium lead dating of mesosiderite zircons by isotope dilution thermal ionization mass spectrometry to reveal an initial crust formation 4 558 5 2 1 million years ago and metal silicate mixing at 4 525 39 0 85 million years ago the two distinct ages coincide with the timing of the crust formation and a large scale reheating event on the eucrite parent body probably the asteroid vesta this chronological coincidence corroborates that vesta is the parent body of mesosiderite silicates mesosiderite formation on vesta can be explained by a hit and run collision 4 525 4 million years ago that caused the thick crust observed by nasa s dawn mission and explains the missing olivine in mesosiderites howardite eucrite diogenite meteorites and vestoids mesosiderite meteorites may originate from a hit and run impact on the parent asteroid of eucrite meteorites probably vesta as mesosiderite zircon u pb ages are found to coincide with those for eucrites

the polymict eucrites elephant moraine a79004 and a79011 and the regolith history of a basaltic achondrite parent body the achondrites elephant moraine a79004 and a79011 are closely related polymicteucrites of a type previously unrecognized in antarctica they contain an early metamorphically homogenized breccia containing clasts of great textural diversity very similar to those in howardites and a late injected mafic clast component that contains a suite of basalts that may in part be the result of impact melting rather than internal igneous processes the basaltic achondrite parent body bap of which they are regolith samples had a complex igneous history of 1 early igneous activity 2 brecciation to form polymict breccias 3 localized metamorphism resulting in partial homogenization of areas of the regolith 4 late igneous activity resulting from internal igneous or impact melting processes and 5 further brecciation and mixing of late formed mafic rocks with early breccias

the genesis of diogenites and hed parent body petrogenesis abstract samples of clasts and whole rocks from eighteen of the twenty four known diogenites orthopyroxenite breccia meteorites have been studied by combined inaa empa in order to elucidate their petrogenetic history the incompatible elements a12o3 and tio2 are positively correlated in diogenite orthopyroxenes these elements determined by empa are also positively correlated with incompatible trace elements such as yb determined by inaa on bulk samples these correlations indicate that most diogenites may form a single igneous fractionation sequence the incompatible minor and trace elements are decoupled from the major elements for essentially constant mg tio2 varies by about 4 times and yb by about 8 times hence there is no strong evidence for igneous fractionation preserved in the major element composition of orthopyroxenes geothermometry calculations using two pyroxene and spinelorthopyroxene thermometers show that these phases in diogenites maintained equilibrium to temperatures in the range 650 880 c far below likely magmatic temperatures in some diogenites orthopyroxenes of differing composition are in breccia contact therefore the low equilibration temperatures were achieved in the diogenites prior to brecciation decoupling of major and trace elements was most likely caused by slow subsolidus cooling in the diogenite pluton which allowed ca fe and mg to reach diffusive equilibration incompatible trace elements likely have much lower diffusivities in orthopyroxene and therefore may have largely preserved their magmatic distributions the extensive variation in incompatible trace elements indicates that either the diogenites were formed through an extensive crystallization interval or that partition coefficients greatly increased during crystallization if the former were true one would expect to find substantial amounts of plagioclase in the diogenites if they are comagmatic with eucrites this is contrary to observations a model in which diogenites crystallized from one or more melts of approximately orthopyroxenitic composition can satisfy both the mineralogie and trace element constraints

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

clay mineraloid weathering products in antarctic meteorites abstract clay mineraloids are associated with gypsum k fe sulfates possibly jarosite cryptocrystalline rust and possibly with zeolites and or secondary alkali feldspars as terrestrial weathering products in stony meteorites from the allan hills alh and elephant moraine eet collection areas in victoria land antarctica weathering formed fracture fillings in fusion crusts of eucrites eeta79004 and eeta79005 diogenites alha77256 and eeta79002 shergottite eeta79001 and h5 chondrite alh82102 and decomposition products of glass and plagioclase in interior samples of achondrites clay mineraloids displayed massive to incipient vermicular forms with elemental compositions that suggest smectite and mica like phases deposits were too small to yield pure material for phase identification although x ray diffractometry and differential scanning calorimetry of bulk samples suggested that the clay mineraloids were not well crystallized a typical structural formula calculated on a smectite basis follows k 0 26 ca 0 04 al 0 97 ti 0 02 fe 3 0 77 mg 0 03 si 4 00 o 10 oh 2 n 2 o net charge 0 28 excessions 0 58 si 0 02 cl 0 09 so 4 0 02 po 4 hydrocryogenic diagenesis can initiate clay mineral formation on timescales of 10 4 10 6 y even with only limited supplies of liquid water cosmochemists must take care not to confuse possible weathering induced elemental and isotopic fractionations in antarctic meteorite samples with signatures of pre terrestrial cosmic processes given proper sample selection and testing though occurrence of clay mineraloid and other weathering products should probably not impede progress in studies of antarctic meteorites

corrosion of fe ni alloys by cl containing akaganeite beta feooh the antarctic meteorite case a suite of 12 iron and 8 stony meteorites from various environments and locations in antarctica was studied representing a range of compositions metallographic structures and degrees of weathering polished sections of meteoritic metal with adhering corrosion products were examined microscopically with the electron microprobe and sem and were used as samples for x ray diffraction examination the major corrosion products are cl containing akaganeite up to 5wtper thousand cl and goethite with minor amounts of lepidocrocite and maghemite cl is not native to the meteorites but owing to the electrochemical nature of the corrosion of fe ni alloys is attracted from the snow and ice or rocky soil environment that contains low amounts of cl akaganeite precipitates near the reaction front incorporating cl ions into ion exchange sites where they may be retained made available for further depassivating corrosive action or become flushed from the system with time and distance from the reaction surface akaganeite ages and transforms to mainly goethite and maghemite it is again argued that lawrencite fecl 2 is not a mineral in meteorites in the stormy antarctic wind blown terrestrial particles may become attached to the weathering products on the meteorite and in time themselves decompose delivering terrestrial ions to the meteorite corrosion system the ions may move a significant distance from the surface and in particular cl may be found along almost invisible cracks in the deep interior trace element work and age determinations 36 cl should take this problem into account

terrestrial 81kr kr ages of antarctic meteorites the production rate of 38ar in meteorites p 38 has been determined as a function of the sample s chemical composition from 81kr kr exposure ages of four eucrite falls the cosmogenic 78kr 83kr ratio is used to estimate the shielding dependence of p 38 from the true 38ar exposure ages and the apparent 81kr kr exposure ages of nine antarctic eucrite finds terrestrial ages are calculated they range from about 3 105a pecora escarpment 82502 to very recent falls thiel mountains 82502 polymict eucrites from the allan hills a78132 a79017 and a81009 have within the limits of error the same exposure age 15 2 106a and the same terrestrial age 1 1 105a this is taken as strong evidence that these meteorites are fragments of the same fall a similar case are the elephant moraine polymict eucrites a79005 a79006 and 82600 with an exposure age of 26 106a and a terrestrial age of 1 8 105a eeta79004 may be different from this group because its exposure age and terrestrial age are 21 106a and 2 5 105a respectively the distribution of terrestrial ages of allan hills meteorites is discussed meteorites from this blue ice field have two sources directly deposited falls and meteorites transported to the allan hills inside the moving antarctic ice sheet during the surface residence time meteorites decompose due to weathering processes the weathering half life is about 1 6 105a from the different age distributions of allan hills and yamato meteorites it is concluded that meteorite concentrations of different antarctic ice fields need different explanations

absorption bands near three micrometers in diffuse reflectance spectra of carbonaceous chondrites comparison with asteroids abstract we measured infrared diffuse reflectance spectra of several carbonaceous chondrites in order to obtain additional information on the surface materials of their presumed parent bodies c type asteroids the presence and intensity of absorption bands near 3 m in the reflectance spectra are due to the presence and abundance of hydrates and or hydroxyl ions the absorption features of the 3 m hydration bands of carbonaceous chondrites were compared with those of asteroids 1 ceres and 2 pallas they are commonly classified into separate subtypes g and b type the spectral shapes of pallas and renazzo cr2 chondrite around the 3 m absorption band are an excellent match this result may suggest that the amount of hydrous minerals in the surface material of pallas is smaller than that in the cm2 or ci chondrites and the hydrous minerals on the surface of pallas may be similar to those found in renazzo the spectral features around the 3 m band of ceres are different from those of carbonaceous chondrites studied in this paper

the polymict eucrites the polymict eucrites are a suite of about 14 polymict achondritic meteorites that contain at least 90 vol of eucritic material and are found both in antarctica and elsewhere they are part of a continuum of polymict breccias that includes howardites and polymict diogenites rare gas data suggest that some are gas rich regolith breccias the clasts contained in polymict eucrites sample a variety of lithologies from their parent body and include eucritic clasts alkali enriched eucrites pyroxene cumulate eucrites two pyroxene mafic rocks possibly feldspar cumulate eucrites diogenites fayalitic lithologies and a variety of other mineral clasts the eucritic clasts are probably samples of near surface lithologies on the parent body but the presence of two pyroxene mafic rocks is considered to be evidence of magmatic activity at pressures in excess of 1 kbar in the parent body partial melt models may explain some of the diversity among the clasts but cumulus processes are believed to have been important if pressures greater than 1 kbar are confirmed then the basaltic achondrite parent body bap must have a diameter in excess of 200 km the variety of lithologies suggests that not all basaltic achondrites are samples of igneous rocks formed by single stage melting of a chondritic asteroid but are instead samples of an evolved and diverse crust produced by serial magmatism

the composition of the mantle of the eucrite parent body and the origin of eucrites abstract previous estimates of the composition of the epb have tacitly assumed chondritic abundances of refractory lil elements a model is presented here which utilizes refractory element ratios instead consideration of these ratios and of known olivine liquid partition coefficients for sc mg and si imply that the epb mantle may be accurately modeled as a simple mixture of 25 eucrite 75 olivine the model also implies that eucrites such as juvinas and sioux county were derived by large degrees of partial melting 20 30 comparison of the model epb mantle to known meteorite classes indicates a similarity between the element abundances of the epb and c3 chondrites

petrographic chemical and spectroscopic evidence for thermal metamorphism in carbonaceous chondrites i ci and cm chondrites abstract we present a comprehensive description of petrologic chemical and spectroscopic features of thermally metamorphosed ci like and cm and cm like chondrites only two such ci chondrites have so far been discovered i e y 86029 and y 82162 thermal metamorphism in these chondrites is apparent in their low contents of h2o c and the most thermally labile trace elements partial dehydration of matrix phyllosilicates and abundance of thermally decomposed ca mg fe mn carbonates which apparently resulted from heating of mg fe carbonate precursors the cm chondrites exhibit a wide range of aqueous and thermal alteration characteristics this alteration was almost complete in y 86720 and y 86789 which also escaped alternating episodes of oxidation and sulfidization experienced by the others thermal metamorphism in the cm chondrites is apparent in loss of thermally labile trace elements and also in partial to almost complete dehydration of matrix phyllosilicates heating was less uniform in them than in ci chondrites this dehydration is also evident in strength and shapes of integrated intensities of the 3 m bands except in pca 91008 which experienced extensive terrestrial weathering tochilinite is absent in all but y 793321 probably due to heating textural evidence for thermal metamorphism is conspicuous in blurring or integration fusion of chondrules with matrix in the more extensively heated 600 c cm chondrites like pca 91008 and b 7904 tem and xrd analyses reveal that phyllosilicate transformation to anhydrous phases proceeds via poorly crystalline highly desiccated and disordered intermediate phases in the least and moderately heated 400 600 c carbonaceous chondrites like wis 91600 pca 91008 and y 86029 these findings are significant in that they confirm that these phases occur in meteorites as well as terrestrial samples thermal alteration in these meteorites can be used to identify other carbonaceous chondrites that were thermally metamorphosed in their parent bodies combining rnaa trace element data for experimentally heated murchison cm2 samples with petrographic and spectroscopic data these thermally metamorphosed carbonaceous chondrites can be ordered by severity of open system heating as 400 c y 793321

the antarctic achondrite alha 76005 a polymict eucrite abstract alha 76005 is a basaltic achondrite containing few if any orthopyroxenes its bulk major and trace element composition is like that of a non cumulate eucrite and unlike that of a howardite it contains a variety of igneous clasts which differ in their textures pyroxene plagioclase ratios and pyroxene and plagioclase compositions one clast no 4 was found to have the ree pattern of a cumulate eucrite and an oxygen isotopic composition different from that of the bulk meteorite both the chemical and oxygen isotopic composition of clast no 4 suggest that it was derived from a source different from its host these observations lead to the conclusion that alha 76005 is a polymict eucrite

experimental investigation of the partitioning of phosphorus between metal and silicate phases implications for the earth moon and eucrite parent body abstract the solid metal silicate melt partition coefficient for p d p has been determined experimentally at 1190 c and 1300 c the dependence of the partition coefficient on oxygen fugacity has been investigated and is consistent with a valence state of 5 for p in the silicate melt the experimental partition coefficients are given by log d p 1 21 log o 2 15 95 at 1190 c log d p 1 53 log o 2 17 73 at 1300 c the experimentally determined partition coefficients may be used to interpret the low p la ratios of the earth moon and eucrites relative to c1 chondrites the low p la ratios in the eucrites may be explained by partitioning of p into 5 to 25 of a sulfur bearing metallic liquid assuming equilibration and separation of the liquid metal from the silicates at low degrees of partial melting of the silicates the low w la ratios in the eucrites compared to c1 chondrites require the separation of an additional 2 to 10 solid metal the lowering of both p la and w la ratios in the moon may be explained by partitioning of p and w into metal during formation of a small core by separation of liquid metal from silicate at low degrees of partial melting of the silicates the w la ratios in the earth and moon are virtually indistinguishable while p la ratios differ by a factor of two the concentrations of feo also appear to be different these observations are difficult to reconcile with the hypothesis of a terrestrial origin of the moon following formation of the earth s core but are consistent with independent formation of the earth and moon

mixing depths and sediment accumulation rates on an arid tropical shelf based on fine fraction 210pb analysis abstract continental shelves in arid tropical settings present particular challenges to 210pb based analysis of sedimentation rates and surface mixing owing to the combination of coarse sediment deep and year round bioturbation and lower atmospheric flux of 210pb the modern continental shelf at the northern terminus of the hyper arid gulf of eilat aqaba goe receives flood runoff of siliciclastics producing a mixed seabed with 20 carbonate that is dominated by larger benthic foraminifera and mollusks focusing analysis on only the fine fraction of deep penetrating cores 70 cm from 15 to 40 m water depths yields reliable 210pb profiles in contrast to analysis of bulk sediment graphical abstract sedimentation rates increase offshore five fold from 0 01 0 04 cm y in 15 m water depth to 0 21 0 27 cm y in 30 40 m depths reflecting offshore redistribution of flood delivered siliciclastic sediments away from the wadi mouth a result also supported by an offshore increase in the inventory of excess 210pb in contrast the thickness of the surface mixed layer sml decreases from 30 cm to 20 cm with proximity to anthropogenic stressors channelized flood runoff historic release of sewage and operation of fish cages which we attribute to the suppression of macrobenthic burrowers the rate of sedimentation on the gulf shelf away from dynamic bypassing in the 15 m shoreface is comparable to other tropical carbonate shelves rich in large benthic foraminifera and is higher than rates documented on the adjacent slope increasing confidence in this approach to 210pb analysis using only the fine fraction analysis of the fine fraction rather than bulk sediment would be a useful adjustment to 210pb methodology in any area with scarce fine grained sediment

differences in the degree of weathering between antarctic and non antarctic meteorites inferred from infrared diffuse reflectance spectra abstract infrared diffuse reflectance spectra were measured for antarctic and non antarctic meteorites to compare the degree of terrestrial weathering by using the integrated intensity of absorption bands near 3 m caused by hydrous minerals and the intensity of absorption bands near 7 4 m 1350 cm 1 probably caused by hydrous carbonates non antarctic ordinary chondrite finds usually show large values of the integrated intensity of the 3 m band whereas non antarctic ordinary chondrite falls show small intensities some antarctic ordinary chondrites are as fresh as non antarctic ordinary chondrite falls in the sense of the integrated intensity of the 3 m band some antarctic eucrites show large values of the integrated intensity of the 3 m band although the degree of weathering on the a b c scale is reported to be a weathering produced hydrous carbonates seem to be ubiquitous in antarctic ordinary chondrites because the spectra of all the antarctic ordinary chondrites measured show the presence of the 7 4 m band non antarctic ordinary chondrite falls show very weak 7 4 m bands suggesting only little weatheringproduced hydrous carbonates diffuse reflectance spectra were also measured for the mixtures of akaganeite goethite artinite or calcite with the nuevo mercurio h5 ordinary chondrite to examine spectral changes and to compare them with those of meteorites absorption bands near 7 m of diffuse reflectance spectra are sensitive to the presence of carbonates

coherence between solar activity and the east asian winter monsoon variability in the past 8000 years from yangtze river derived mud in the east china sea ams 14 c dating and grain size analysis for core pc 6 located in the middle of a mud area on the inner shelf of the east china sea ecs were used to rebuild the holocene history of the east asian winter monsoon eawm the 7 5 m core recorded the history of environmental changes during the postglacial transgression the core s mud section the upper 450 cm has been formed mainly by suspended sediment delivered from the yangtze river mouth by the ecs winter coastal current ecswcc since 7 6 kyr bp using a mathematical method called grain size vs standard deviatiow we can divide the core pc 6 s grain size distribution into two populations at about 28 mu m the fine population 28 mu m is considered to be transported by the ecswcc as suspended loads content of the fine population changes little and represents a stable sedimentary environment in accord with the present situation thus variation of mean grain size from the fine population would reflect the strength of ecswcc which is mainly controlled by the east asian winter monsoon abrupt increasing mean grain size in the mud section is inferred to be transported by sudden strengthened ecswcc which was caused by the strengthened eawm thus the high resolution mean grain size variation might serve as a proxy for reconstruction of the eawm a good correlation between sunspot change and the mean grain size of suspended fine population suggests that one of the primary controls on centennial to decadal scale changes of the eawm in the past 8 ka is the variations of sun irradiance i e the eawm will increase in intensity when the number of sunspots decreases spectral analyses of the mean grain size time series of core pc 6 show statistically significant periodicities centering on 2463 1368 128 106 100 88 91 7678 and 70 72 years the eawm and the east asian summer monsoon easm agree with each other well on these cycles and the east asian monsoon eam and the indian monsoon also share in concurrent cycles in holocene which are in accord with the changes of the sun irradiance c 2005 elsevier b v all rights reserved

seamount topography by least squares inversion of altimetric geoid heights and shipborne profiles of bathymetry and or gravity anomalies summary altimetric measurements of sea surface heights have long been used to locate uncharted marine features newly available data sets geosat gm ers 1 and topex poseidon now allow the topography of submarine volcanoes to be accurately restored and a method based upon inverse modelling is presented in this paper this method allows a joint assimilation of altimetric data and shipborne profiles of bathymetry and or gravity anomalies when available furthermore uncertainties can be computed together with the topography which constitutes a noticeable improvement since these parameters are still missing in the usual bathymetric data bases tests are performed using simulated data in order to characterize the errors which may or must occur with the modelled topography of a previously unknown volcano in particular the errors due to data uncertainties and the lack of precise knowledge of sensitive parameters that are used in the modelling these errors can be maintained under the 100 m level rms for altimetric data with a measurement noise of 5 cm rms or less which is achieved for geosat ers 1 and topex poseidon altimeters an example of inversion of seasat data is presented in the case of a seamount in french polynesia

tidal fluxes of nutrients and suspended sediments at the north inlet winyah bay national estuarine research reserve beginning june of 1993 suites of 13 water samples have been collected at oyster landing north inlet sc every 20 days covering two consecutive tidal cycles at 2 07 h intervals in order to ascertain whether this large and still growing water chemistry data set can be used to determine tidal fluxes of nutrients and sediments we coupled measured concentrations to estimates of instantaneous tidal discharge based on a basin water storage curve and hindcast tides the mean advective fluxes of all constituents including salt showed statistically significant exports this result however is largely due to an ebb bias in the sampling protocol which resulted in 52 of the samples being collected on ebb tide versus a theoretical percentage of 48 when this bias was corrected by reducing the mean discharge 610 l s 1 to a value 125 l s 1 that produced a balance between the mean advective and dispersive salt fluxes the advective fluxes of the other constituents were reduced to values that are not significantly different from zero in addition to a statistically significant dispersive influx of salt significant dispersive exports were found for don nh4 dop po4 and doc all particulate constituents pn pp iss and oss yielded dispersive fluxes that were not significantly different from zero annual material budgets for the oyster landing basin based on the dispersive fluxes of all constituents except salt are generally similar in magnitude and direction to those measured by dame r f spurrier j d williams t m kjerfve b zingmark r g wolaver t g chrzanowski t h mckeller h n vernberg f j 1991 annual material processing by a salt marsh estuarine basin in south carolina usa marine ecology progress series 72 153e166 in the nearby and ecologically similar bly creek basin indicating that the dispersive fluxes determined in this study are realistic we offer suggestions for improving the reliability and usefulness of future oyster landing water quality data 2006 elsevier ltd all rights reserved

light rare earth element enrichments in ureilites a detailed ion microprobe study this paper explores the possible origin of the light rare earth element lree enrichments observed in some ureilites a question that has both petrogenetic and chronologic implications for this group of achondritic meteorites rare earth element and other selected elemental abundances were measured in situ in 14 thin sections representing 11 different ureilites the spatial microdistributions of rees in c rich matrix areas of the three ureilites with the most striking v shaped whole rock ree patterns kenna goalpara and novo urei were investigated using the ion imaging capability of the ion microprobe all olivines and clinopyroxenes measured have lree depleted patterns with little variation in ree abundances despite large differences in their major element compositions from ureilite to ureilite furthermore we searched for but did not find any minor mineral phases that carry lrees the only exception is one ti rich area 20 m in lewis cliff lew 85400 with a major element composition similar to that of titanite ree abundances in this area are high ranging from la 400 ci to lu 40 ci in contrast all ion microprobe analyses of c rich matrix in kenna goalpara and novo urei revealed large lree enrichments in addition c rich matrix areas in the three polymict ureilites elephant moraine eet 83309 eet 87720 and north haig which have less pronounced v shaped whole rock ree patterns show smaller but distinct lree enrichments the c rich matrix in antarctic ureilites tends to have much lower lree concentrations than the matrix in non antarctic ureilites there is no obvious association of the lrees with other major or minor elements in the c rich areas ion images further show that the lree enrichments are homogeneously distributed on a microscale in most c rich matrix areas of kenna goalpara and novo urei these observations suggest that the lrees in ureilites most probably are absorbed on the surface of fine grained amorphous graphite in the c rich matrix it is unlikely that the lree enrichments are due to shock melts or are the products of metasomatism on the ureilite parent body we favor lree introduction by terrestrial contamination

along channel flow and sediment dynamics at north inlet south carolina in may of 2005 an observational program was carried out to investigate the along channel hydrodynamics and suspended sediment transport patterns at north inlet south carolina along channel variability which is important in establishing sediment transport pathways has not been characterized for this system measurements of water column currents salinity bed sediment suspended sediment concentration and particle size distribution were obtained over a complete tidal cycle along the thalweg of the inlet entrance along channel currents shear stress and bed sediment distributions vary significantly in space and time along a 3 km section bracketing the inlet throat most of the variability is consistent with geomorphic controls such as bed elevation variability and channel width the highest velocities shear stresses suspended sediment concentration and bed sediment grain size are observed in the narrowest section of the inlet throat magnitudes systematically decrease along the channel toward the marsh as changes in channel geometry and branching reduces flow energy due to tidal asymmetry the ebb phase contains significantly higher currents and associated sediment transport over the complete tidal cycle depth integrated transport is directed towards the marsh landward of the intersection of town and debidue creek in contrast net transport is out of the inlet seaward of this intersection sediment grain size distributions show 35 more material less than 63 m on flood suggesting net landward transport of fines

40ar 39ar dating of microgram feldspar grains from the paired feldspathic achondrites gra 06128 and 06129 abstract 40 ar 39 ar ages of single feldspar grains from the paired meteorites graves nunatak 06128 gra8 8 grains and 06129 gra9 26 grains are presented plateau ages 70 of the 39 ar released ranged from 4000 to 4600 ma with an average 1 uncertainty of 90 ma the most precise ages obtained were 4267 17 ma for a grain from gra8 and 4437 19 ma and 4321 18 ma for two grains from gra9 isotope correlation diagrams yield less precise ages ranging from 3800 to 5200 ma with an average 1 uncertainty of 250 ma they indicate a negligible trapped component plateau ages integrated total fusion ages and isochron ages are internally concordant at the 95 confidence level the distribution of the plateau ages for gra9 is bimodal with peaks at 4400 and 4300 ma in contrast the plateau age distribution for gra8 peaks at about 4260 ma with broad wings extending toward younger and older ages to explain the distributions of grain ages we prefer a scenario that includes a major post formation event about 4400 ma ago and a later melt intrusion event that heated gra8 more than some parts of gra9

compositions and taxonomy of 15 unusual carbonaceous chondrites abstract we used instrumental neutron activation analysis and petrography to determine bulk and phase compositions and textural characteristics of 15 carbonaceous chondrites of uncertain classification acfer 094 type 3 0 ungrouped cm related belgica 7904 mildly metamorphosed anomalous cm like chondrite possibly a member of a new grouplet that includes wisconsin range wis 91600 dhofar 225 and yamato 86720 dar al gani dag 055 and its paired specimen dag 056 anomalous reduced cv3 like dag 978 type 3 ungrouped dominion range 03238 anomalous magnetite rich co3 1 elephant moraine 90043 anomalous magnetite bearing co3 graves nunataks 98025 type 2 or type 3 ungrouped grosvenor mountains gro 95566 anomalous cm2 with a low degree of aqueous alteration hammadah al hamra hah 073 type 4 ungrouped possibly related to the coolidge loongana c l 001 grouplet lewis cliff lew 85311 anomalous cm2 with a low degree of aqueous alteration northwest africa 1152 anomalous cv3 pecora escarpment pca 91008 anomalous metamorphosed cm queen alexandra range 99038 type 2 ungrouped sahara 00182 type 3 ungrouped possibly related to hah 073 and or to c l 001 and wis 91600 mildly metamorphosed anomalous cm like chondrite possibly a member of a new grouplet that includes belgica 7904 dhofar 225 and y 86720 many of these meteorites show fractionated abundance patterns especially among the volatile elements impact volatilization and dehydration as well as elemental transport caused by terrestrial weathering are probably responsible for most of these compositional anomalies the metamorphosed cm chondrites comprise two distinct clusters on the basis of their 17o values approximately 4 for pca 91008 gro 95566 dag 978 and lew 85311 and approximately 0 for belgica 7904 and wis 91600 these six meteorites must have been derived from different asteroidal regions

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

concentrations of siderophile elements in nonmagnetic fractions of antarctic h and l chondrites a quantitative approach on weathering effects the nonmagnetic separates of antarctic h and l chondrite finds from the lewis cliff stranding area are enriched in fe and siderophile elements such as ni co cu as ir and au relative to those of non antarctic falls the siderophile enrichments are caused by the oxidation of metallic fe ni to nonmagnetic hydrous fe ni oxides the concentrations of fe ni and co in each sample were used to calculate the amount of oxidized metal which serves as a quantitative measure of the degree of weathering the amount of oxidized metal is generally between 1 10 wt and shows a rough correlation with the qualitative a b c weathering classification for increasing rustiness no clear correlation was found between weathering and terrestrial age although meteorites older than 0 2 ma contain on the average 50 more oxidized metal also no correlation was found between the degree of weathering and the natural thermoluminescence tl level which is dominated by the thermal history in space rather than by the thermal history in or on the antarctic ice the only significant parameter for the degree of weathering seems to be the location of find with the most weathered specimens being found in a part of the stranding area where melt water ponds are known to occur this observation confirms that the occasional presence of liquid water plays an important role in the antarctic weathering process and explains the poor correlation of the degree of weathering of antarctic meteorites with terrestrial age and surface exposure age

comparisons of antarctic and non antarctic achondrites and possible origin of the differences abstract in order to discuss differences between antarctic and non antarctic achondrites we investigated pairing of mainly the yamato achondrites by mineralogical techniques in addition to five paired specimens of the y74159 type polymict eucrites three new groups distinct from the y74159 type have been recognized one group y791960 of howarditic polymict eucrites is similar to those of non antarctic origin some antarctic monomict eucrites differ in texture and chemistry from the non antarctic specimens more than 50 diogenite specimens recovered from the yamato bare ice field can be grouped into two falls of separate locations compared with 8 from the usa collection and 9 from the non antarctic groups thirty antarctic ureilites are separate falls 2 pairings and their individual masses are small these observations suggest that discussion of differences between the antarctic and non antarctic achondrites largely depends on detection of pairings of the antarctic specimens the pairings of the specimens from victoria land have not been as well characterized as those of the yamato mountains comparisons with non antarctic meteorites show that the antarctic heds and ureilites differ from non antarctic specimens by the following criteria 1 1 polymict eucrites excluding those with howarditic affinity have not been found in the non antarctic collections 2 2 magnesian ureilites and augite bearing ureilites were found only in antarctica the differences may not be attributed to just one factor the above evidence of two unique diogenite falls preserved on the restricted ice fields suggests that the yamato diogenites may represent falls on restricted areas in the distant past the discovery of many small unique eucrites and ureilites suggests that within the large number of small specimens on a bare ice field there is a higher chance of finding unique varieties

seabed texture and composition changes offshore of port royal sound south carolina before and after the dredging for beach nourishment abstract beach nourishment has been a strategy widely used to slow down coastal erosion in many beaches around the world the dredging of sand at the borrow site however can have complicated physical geological and ecological impacts our current knowledge is insufficient to make accurate predictions of sediment infilling in many dredging pits due to lack of detailed sediment data two sites in the sandy shoal southeast of port royal sound prs of south carolina usa were sampled 8 times from april 2010 to march 2013 one site defined as borrow site was 2 km offshore and used as the dredging site for beach nourishment of nearby hilton head island in beaufort county south carolina and the other site defined as reference site was 10 km offshore and not directly impacted by the dredging a total of 184 surficial sediment samples were collected randomly at two sites during 8 sampling periods most sediments were fine sand with an average grain size of 2 3 phi and an organic matter content less than 2 after the dredging in december 2011 january 2012 sediments at the borrow site became finer changing from 1 0 phi to 2 3 phi and carbonate content decreased from 10 to 4 changes in mud content and organic matter were small compared with the reference site the borrow site experienced larger variations in mud and carbonate content an additional 228 sub samples were gathered from small cores collected at 5 fixed stations in the borrow site and 1 fixed station at the reference site 0 3 6 9 and 12 months after the dredging these down core sub samples were divided into 1 cm slices and analyzed using a laser diffraction particle size analyzer most cores were uniform vertically and consisted of fine sand with well to moderately well sorting and nearly symmetrical averaged skewness based on the analysis of grain size populations 2 phi and 3 phi sized sediments were the most dynamic sand fractions in prs mud deposition on shoals offshore of prs presumably happens when offshore mud transport is prevalent and there is a following rapid sand accumulation to bury the mud however in this borrow site there was very little accumulation of mud this will allow the site to be used in future nourishment projects presuming no accumulation of mud occurs in the future

grosvenor mountains 95 howardite pairing group insights into the surface regolith of asteroid 4 vesta regolithic howardites are analogs for the surface materials of asteroid 4 vesta recently mapped by the dawn spacecraft rigorously evaluating pairing of howardites recovered in 1995 in the grosvenor mountains gro 95 antarctica enables an examination of a larger more representative regolith sample previous work on two of the howardites studied here concluded that gro 95602 and gro 95535 are solar wind rich surface regolith samples and that they are not paired with each other leading to uncertainty regarding pairing relationships between the other gro 95 howardites based on petrology cosmic ray exposure history and terrestrial age four gro 95 howardites are paired the paired howardites gro 95534 95535 95574 95581 were from a meteoroid with radius of 10 15 cm a preatmospheric size comparable to that of kapoeta the largest known regolithic howardite the paired gro 95 howardites contain clasts of at least 18 separate hed lithologies providing evidence they were assembled from diverse source materials the total eucrite diogenite mixing ratio ratio of all eucrite lithologies to all diogenite lithologies in the paired gro 95 howardites is 2 1 petrographically determined basaltic eucrite cumulate eucrite ratios in regolithic howardites studied here and previously vary more widely than total eucrite diogenite ratios relative to eucritic pyroxene plagioclase is depleted in these howardites which provides evidence that plagioclase is preferentially comminuted in the vestan regolith the extent of plagioclase depletion could be an indicator of regolith maturity

hydration bands near 3 μm and weathering of some antarctic meteorites abstract we studied the degree of weathering of some antartctic meteorites using the integrated intensity of absorption bands hydration bands near 3 m due to the presence of hydrous minerals the allan hills meteorites measured show stronger integrated intensities than the yamato meteorites measured although the number of meteorites we measured is small this suggests that the allan hills meteorites are more weathered than the yamato meteorites the allan hills meteorites show greater terrestrial ages than other antarctic meteorites on the basis of cosmic ray produced nuclide data our results are consistent with the terrestrial age data because weathering produces hydrous minerals integrated intensities near 3 m vary widely among the antarctic meteorites reported to be relatively little weathered under microscopic observation the integrated intensity of hydration bands near 3 m may have the potential for quantifying the degree of weathering these quantified data may help in selecting less weathered meteorites from among the antarctic meteorite collection and may be combined with terrestrial age data to study terrestrial histories of antarctic meteorites

basaltic volcanism on the eucrite parent body petrology and chemistry of the polymict eucrite alha80102 the polymict eucrite meteorite alha80102 i s an unequilibrated breccia of basaltic and gabbroic clasts in a fragmental matrix clasts include basalts of many textural types cumulate gabbro black glass and ferroan troctolite plagioclase silica fe rich olivine ilmenite mesostasis ferroan troctolite has not been previously reported from eucrites or howardites it is interpreted as the end product of fractional crystallization of eucritic magmas bulk and trace element compositions by electron microprobe and inaa of clasts and matrix from alha80102 are similar to those of other eucrites the meteorite contains clasts similar to juvinas and to stannern a clast of cumulate eucrite gabbro is enriched in the light rare earths la lu 2xci this clast is interpreted as an unrepresentative sample of metamorphically equilibrated gabbro lree enriched magmas need not be invoked alha80102 is similar to other polymict eucrites from the allan hills and may be paired with alha76005 alha77302 and alha78040

the sextilia region on asteroid 4vesta stratigraphy and variegation abstract mapping vesta surface composition in the sextilia region offers the unique possibility to investigate stratigraphic relationship of the surface compounds throughout the transition from rheasilvia vesta s prominent impact basin to vesta s northern equatorial region the vir data point to an upper eucrite dominated layer overlaying extended deposits of diogenite in the subsurface which reaches the surface at matronalia rupes the uplifted rim of the rheasilvia impact structure the dominance of diogenite in matronalia rupes suggests the existence of an extended diogenite rich layer and supports the magma ocean model as the most plausible formation model for vesta s interior local enrichment of diogenite outside of the rheasilvia impact basin are interpreted as outcrops of diogenite dominated breccia excavated during the rheasilvia impact event and re excavated by more recent impacts on the contrary the asymmetry in the distribution of diogenite rich outcrops in the norther parts i e the depletion of these deposits in the veneneia region is at odds with the equally distributed plutonic intrusions of diogenite rich material as proposed in the serial magmatism model but could be explained by an uneven distribution of its ejecta on vesta s surface due to an oblique rheasilvia impact

a magma ocean on vesta core formation and petrogenesis of eucrites and diogenites abstract available evidence strongly suggests that the hed howardite eucrite diogenite meteorites are samples of asteroid 4 vesta abundances of the moderately siderophile elements ni co mo w and p in the hed mantle indicate that the parent body may have been completely molten during its early history during cooling of a chondritic composition magma ocean equilibrium crystallization is fostered by the suspension of crystals in a convecting magma ocean until the crystal fraction reaches a critical value near 0 80 when the convective system freezes and melts segregate from crystals by gravitational forces the extruded liquids are similar in composition to main group and stannern trend eucrites and the last pyroxenes to precipitate out of this ocean before convective lockup span the compositional range of the diogenites subsequent fractional crystallization of a main group eucrite liquid which has been isolated as a body of magma produces the nuevo laredo trend and the cumulate eucrites the predicted cumulate mineral compositions are in close agreement with phase compositions analyzed in the cumulate eucrites thus eucrites and diogenites are shown to have formed as part of a simple and continuous crystallization sequence starting with a magma ocean environment on an asteroidal size parent body that is consistent with vesta

comparison of yamato and victoria land polymict eucrites a view from mineralogical and isotopic studies new interior samples of four yamato polymict eucrites y74159 y74450 y75011 and y75015 have been studied by electron microprobe transmission electron microscope and x ray diffraction techniques and compared with several samples of the victoria land polymict eucrites these same samples have been analysed using rb sr and nd sm isotopic systematics several grains of inverted pigeonite with blebby augite similar to those in binda and moama have been identified in all four yamato eucrites coarse grained mesostasis rich subophitic basalts which contain mg rich pigeonite with fe rich olivine veinlets zoned outward to a subcalcic ferroaugite rims have also been found these unique clasts were not found in alh76005 77302 78040 78158 and 78165 and eet eucrites the tight grouping of rb sr and sm nd ratios and similar modal compositions of the yamato group indicate that they are most likely to be pieces from a single fall and distinct from the alh and eet groups however the yamato allan hills and elephant moraine groups may sample a few distinct magmas or similar but different source regions on the same parent body

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

composition and petrology of hed polymict breccias the regolith of 4 vesta the polymict breccias of the howardite eucrite and diogenite hed clan of meteorites preserve records of regolith processes that occur on vesta their putative home world these breccias howardites polymict eucrites and polymict diogenites are impact engendered mixtures of diogenites and eucrites the compositions of polymict breccias can be used to constrain the lithologic diversity of the vestan crust and the excavation depths of these materials we have done petrological and compositional studies of multiple samples of 5 polymict eucrites and 28 howardites to investigate these issues older analyses were done on samples of approx 0 5 gram mass by inaa newer analyses on samples of approx 5 gram mass by xrf and icp ms we estimate the percentage of eucritic material poem of polymict breccias by comparing their al and or ca contents to those of average basaltic eucrite and diogenite our samples have poem ranging from 28 to 98 adding two polymict diogenites from extends the range to poem 10 one hypothesis is that ancient well mixed vestan regolith has poem approx 67 and has a higher content of admixed impactor material several of our howardites have poem of 59 74 al and or ca contents 10 of poem 67 about a third have ni contents 300 micro g g suggesting they contain 2 chondritic material cm and or cr these may be regolithic howardites only one lew 85313 contains ne dominated by a solar wind sw component pca 02066 is dominated by impact melt material of polymict parentage and petrologically appears to be a mature regolith breccia yet it does not contain sw ne gro 95602 falls within the poem window contains sw ne yet has a ni content of 193 micro g g its petrologic characteristics suggest it was formed from immature regolith no polymict breccia clasts no glass trace element characteristics of the polymict breccias demonstrate the dominance of main group eucrites as the basaltic component mixing diagrams of zr nb ba hf and ta with al show no evidence for a significant contribution from stannern trend eucrites an exception is polymict eucrite lew 86001 poem 92 which is dominated by stannern trend basaltic debris howardite lap 04838 poem 84 has higher incompatible trace concentrations than other polymict breccias excluding lew 86001 and either contains a stannern trend basaltic component or has a significant contributions from evolved eucrites like nuevo laredo

complexities in pyroxene compositions derived from absorption band centers examples from apollo samples hed meteorites synthetic pure pyroxenes and remote sensing data we reexamine the relationship between pyroxene composition and near infrared absorption bands integrating measurements of diverse natural and synthetic samples we test an algorithm plc involving a two part linear continuum removal and parabolic fits to the 1 and 2 m bands a computationally simple approach which can easily be automated and applied to remote sensing data employing a suite of synthetic pure pyroxenes the plc technique is shown to derive similar band centers to the modified gaussian model plc analyses are extended to natural pyroxene bearing materials including 1 bulk lunar basalts and pyroxene separates 2 diverse lunar soils and 3 hed meteorites for natural pyroxenes the relationship between composition and absorption band center differs from that of synthetic pyroxenes these differences arise from complexities inherent in natural materials such as exsolution zoning mixing and space weathering for these reasons band center measurements of natural pyroxene bearing materials are compositionally nonunique and could represent three distinct scenarios 1 pyroxene with a narrow compositional range 2 complexly zoned pyroxene grains or 3 a mixture of multiple pyroxene or nonpyroxene components therefore a universal quantitative relationship between band centers and pyroxene composition cannot be uniquely derived for natural pyroxene bearing materials without additional geologic context nevertheless useful relative relationships between composition and band center persist in most cases these relationships are used to interpret m3 data from the humboldtianum basin four distinct compositional units are identified 1 mare humboldtianum basalts 2 distinct outer basalts 3 low ca pyroxene bearing materials and 4 feldspathic materials

lunar and terrestrial crust formation planetary crusts may be accreted produced in primordial differentiation or built up piecemeal by serial magmatism the existence of old polygenetic laterally heterogeneous partial melt rocks in the lunar highlands suggests that the moon produced its early crust by serial magmatism this view can be reconciled with lunar eu anomalies previously thought to support the magma ocean model of crust formation if complications in the fractionation of mare basalts are recognized phase equilibrium and magmatic density information for mare basalts suggest a model in which plagioclase fractionation can occur even though plagioclase is not a near liquidus phase the cryptic fractionation of clinopyroxene in morb provides a precedent for this model the necessity for a lunar magma ocean is questioned but a role for a terrestrial magma ocean of sorts at depth is suggested