late pleistocene and holocene loess sedimentation in central and western qilian shan china revealed by osl dating abstract the knowledge of loess accumulation in the central and western qilian shan was restricted to the time span since 13 11 ka until present loess deposits prior to this period have not yet been reported in this study 23 loess samples from the northern piedmont of central and western qilian shan area have been dated using fine grained quartz optically stimulated luminescence osl dating technique to set up a chronological framework for the loess sedimentation in this region our results demonstrate that the deposition of dust was widespread since the last deglaciation 13 ka until 3 6 ka in the northern piedmont of the central and western qilian shan area furthermore the chronology of the loess sedimentation has been extended back at least to 81 ka which is remarkably older than previously thought the existence of suitable environmental conditions e g vegetation cover for loess accumulation can be deduced in the central and western qilian shan for the holocene and late pleistocene however the loess sedimentation has been revealed to be discontinuous before 13 ka as indicated by its episodic occurrence

bulk chondrite variability in mass independent magnesium isotope compositions implications for initial solar system 26al 27al and the timing of terrestrial accretion abstract we have determined 26 mgdsm 3 the mass independent variations in 26mg 24mg of primitive bulk meteorites to precisions better than 3 ppm 2se our measurements of samples from 10 different chondrite groups show 26 mgdsm 3 that vary from 5 to 22 ppm our data define an array with a positive slope in a plot of 26 mgdsm 3 against 27al 24mg which can be used to determine 26al 27al 0 i e initial 26al 27al and 26 mgdsm 3 0 i e initial 26 mgdsm 3 on such an isochron plot the best fit of our new measurements combined with literature data implies 26al 27al 0 of 4 67 0 78 10 5 and 26 mgdsm 3 0 of 31 6 5 7 ppm 2se for ordinary and carbonaceous chondrites other than cr chondrites which have anomalously low 26 mgdsm 3 these parameters are within uncertainty of those defined by previous measurements of bulk calcium aluminium rich inclusions cais that set canonical 26al 27al 0 5 10 5 the most straightforward interpretation of all these observations is that differences in the al mg of bulk ordinary and carbonaceous chondrites are dominantly controlled by variable contributions of early formed refractory and major silicate components derived from a common canonical reservoir the 26 mgdsm 3 of enstatite chondrites are slightly more radiogenic 3 ppm at similar al mg to the ordinary chondrites we speculate that this is related to the timing of removal of a refractory component from the source reservoirs of these different meteorite groups the higher 26 mgdsm 3 of the enstatite chondrites suggests later 0 5 ma post cais condensation and loss of this refractory component despite inferred consistency of 26al 27al 0 and 26 mgdsm 3 0 across most chondrite groups some nebular heterogeneity is required to account for the compositions of cr chondrites our preferred interpretation is that the cr source region has lower 26 mgdsm 3 0 as the most appropriate isotopic reference for the earth our new mean enstatite chondrite composition allows us to assess possible ingrowth of 26mg from live 26al during accretion of the earth the earth has 26 mgdsm 3 within uncertainty of enstatite chondrites despite its higher al mg this requires that the terrestrial increase in al mg which we attribute to vapour loss during accretion must have happened 1 5 ma post cai formation in an instantaneous fractionation model

thermal history of the h chondrite parent body implications for metamorphic grade and accretionary time scales abstract multiple temperature age constraints for eight h chondrite samples have been used to provide insight into the thermal history of their parent body through combination with numerical models of thermal evolution assuming internal heating by 26al and conductive cooling the effect of spreading accretion out over time is the principal focus of this work a wide range of body size and date of accretion is systematically tested for different values of accretion rate in order to quantify and illustrate the parameter space that is consistent with the available thermo chronological data we conclude that the h chondrite samples considered have a thermal history consistent with a parent body that at some stage had a concentric onion shell internal structure that body had a radius no larger than 130 km and accretion most probably took place over a time interval on the order of 0 0 0 2 myr approximately 2 myr after cai condensation in any case the time interval of accretion is unlikely to have been more than 0 5 myr supporting evidence in favour of rapid accretion possibly through reassembly of the fragments of an earlier generation of bodies furthermore the h chondrites studied here are inferred to have come from a wide depth range within the body where they experienced metamorphism indicating that preservation of the onion shell structure is unlikely the presence of an insulating regolith does not modify this conclusion as appropriate thermal histories for the three h6 samples considered cannot be reproduced at depths near the surface asteroid 6 hebe may be the parent body of the h chondrites but the high bulk density of the latter is difficult to reconcile with a rubble pile structure of pure h chondrite material finally optimized thermal histories are used to constrain the temperatures characterizing boundaries between petrological types 800 1000 and 1140 k for the h3 4 h4 5 and h5 6 boundaries respectively in detail the type 6 samples studied here are inferred to have experienced a similar peak temperature on the order of 1180 k but spent different times at that temperature while samples of lower metamorphic grade experienced different peak temperature but spent more or less the same time within 10 k of peak temperature on the order of 1 ma these results constitute a quantitative framework within which variations in petrographic and textural properties may be interpreted

extending the vostok ice core record of palaeoclimate to the penultimate glacial period the ice core record of local temperature dust accumulation and air composition at vostok station antarctica now extends back to the penultimate glacial period 140 200 kyr ago and the end of the preceding interglacial this yields a new glaciological timescale for the whole record which is consistent with ocean records temperatures at vostok appear to have been more uniformly cold in the penultimate glacial period than in the most recent one concentrations of co2 and ch4 correlate well with temperature throughout the record

differentiation of vesta implications for a shallow magma ocean abstract the dawn mission confirms earlier predictions that the asteroid 4 vesta is differentiated with an iron rich core a silicate mantle and a basaltic crust and supports the conjecture of vesta being the parent body of the hed meteorites to better understand its early evolution we perform numerical calculations of the thermo chemical evolution adopting new data obtained by the dawn mission such as mass bulk density and size of the asteroid we have expanded the thermo chemical evolution model of neumann et al 2012 that includes accretion compaction melting and the associated changes of the material properties and the partitioning of incompatible elements such as the radioactive heat sources advective heat transport and differentiation by porous flow to further consider convection and the associated effective cooling in a potential magma ocean depending on the melt fraction the heat transport by melt segregation is modelled either by assuming melt flow in a porous medium or by simulating vigorous convection and heat flux of a magma ocean with a high effective thermal conductivity our results show that partitioning of 26al and its transport with the silicate melt is crucial for the formation of a global and deep magma ocean due to the enrichment of 26al in the liquid phase and its accumulation in the sub surface for formation times t 0 1 5 ma a thin shallow magma ocean with a thickness of 1 to a few tens of km forms its thickness depends on the viscosity of silicate melt the lifetime of the shallow magma ocean is o 10 4 o 10 6 years and convection in this layer is accompanied by the extrusion of 26al at the surface resulting in the formation of a basaltic crust the interior differentiates from the outside inwards with a mantle that is depleted in 26al and core formation is completed within 0 3 ma the lower mantle experiences a maximal melt fraction of 45 suggesting a harzburgitic to dunitic composition our results support the formation of non cumulate eucrites by the extrusion of early partial melt while cumulate eucrites and diogenites may form from the crystallising shallow magma ocean silicate melt is present in the mantle for up to 150 ma and convection in a crystallising core proceeds for approximately 100 ma supporting the idea of an early magnetic field to explain the remnant magnetisation observed in some hed meteorites

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

a model for planetesimal meltdown by 26al and its implications for meteorite parent bodies the melting of planetesimals heated by 26 al has been modelled using a new finite difference method that incorporates convection as an example we consider a planetesimal with a radius of 64 km which accretes instantaneously at t 0 75 myr after the formation of calcium aluminum rich inclusions from cold 250 k nebular dust with 50 porosity at t 0 9 myr t 700 k the planetesimal shrinks to a radius of 50 km due to sintering at t 1 2 myr t 1425 k the fully insulated interior deeper than a few kilometers starts to melt and at t 1 5 myr t 1725 k with 50 melting convection starts by t 2 myr the planetesimal is a globe of molten convecting slurry inside a thin residual crust from about t 2 5 myr the crust thickens rapidly as the power of 26 al fades planetesimals probably melt in this manner when they accrete before t 1 3 myr and are large enough to insulate themselves r 20 km for accretion at t 0 rising to 80 km at t 1 3 myr melting behavior will also be affected by the level of 60 fe in nebular dust by the extent of devolatilization reactions and basalt segregation during heating and by gradual accretion the model suggests that a the parent bodies of differentiated meteorites had accreted before about t 1 5 to 2 myr and before most chondritic parent bodies had formed and b that molten planetesimals may be a source for chondrule melt droplets

partly pedogenic origin of magnetic variations in chinese loess quaternary sequences of interbedded aeolian silts loess and buried soils palaeosols potentially provide one of the best terrestrial records of past climates1 5 magnetic susceptibility variations in loess and palaeosol sequences from china are strongly correlated with climate induced fluctuations of oxygen isotope ratios in deep sea sediments2 4 6 8 as an explanation of this correlation it has been suggested that the recorded variations in magnetic susceptibility depend primarily on the degree of dilution by non magnetic bulk loess constituents of a uniform magnetic assemblage derived from remote but unknown sources6 8 it has also been suggested that such a model involving changes in the accumulation rate of loess superimposed on a constant flux of magnetic particles provides a relative geological timescale through the control of loess deposition by astronomically modulated climate fluctuations7 here we report a preliminary test of this model using rock magnetic properties especially sensitive to variations in magnetic grain size our results show that palaeosols are characterized by much finer magnetic grain size assemblages than are the intervening loess units this suggests that a simple model based on constant magnetic influx and dilution by variable amounts of non magnetic loess is inadequate our magnetic measurements establish the close comparability of the fine grained magnetic minerals in the palaeosol samples to those in contemporary soils and thus point to a partially pedogenic origin for the magnetic mineral assemblages in the palaeosols

extraterrestrial iridium sediment accumulation and the habitability of the early earth s surface we have measured the concentrations of iridium and platinum in ancient metasediments from akilia island southern west greenland to obtain the first direct constraints on the extraterrestrial mass flux at the earth s surface before 3 8 gyr the lunar impact record indicates this was a time of heavy bombardment the average lunar cratering rate between 4 15 and 3 8 gyr was elevated 150 times the modern value hence heightened ir and pt abundances are possible in sediments from this time however the observed concentrations of ir and pt in the akilia metasediments are extremely low in most samples ir 3 ppt and pt 20 ppt in contrast the average modern crustal abundances of ir and pt are 50 ppt and 2 ppb respectively the very low concentrations observed in the akilia metasediments cherts and banded iron formations can be reconciled with the lunar record by quantifying the effects of sedimentation rate on the efficiency with which the extraterrestrial mass flux is sampled the observations are explained if rapidly accumulating sediments sampled stochastic bombardment by an impactor population governed by a power law mass distribution such that exogenous ir and pt are concentrated in rare horizons the required sedimentation rates are geologically plausible this explanation has two consequences first evidence of massive impact events may be rare in sediments older than 3 8 gyr despite heavy bombardment second conditions at the earth s surface may have been conducive for extensive accumulation of sedimentary sequences and for microbial life during most of the period 4 15 3 8 gyr it is possible that the earth s surface hosted microbial habitats during most of this time if microbes living in deep sea or deep crustal environments survived photic zone vaporizing impacts that would have occurred every 30 myr hence evidence of life is expected even in the earliest sedimentary sequences

thermal evolution model for the h chondrite asteroid instantaneous formation versus protracted accretion abstract we present a model of the thermal evolution of asteroids assuming an onion shell model for the h chondrite parent body we obtain constraints for the h chondrite asteroid parameters by fitting empirical h chondrite cooling ages of estacado guarena kernouve mt browne richardton allegan nadiabondi ste marguerite and forest vale by using a genetic algorithm for parameter optimisation the model improves previous calculations on the thermal history calculated in the instantaneous accretion approximation considering sintering and porosity dependent heat conduction the model is extended to include a finite growth time of the parent body to study whether the meteoritic record constrains the duration of the growth phase of the parent body where it assembles most of its mass it is found that only short accretion times of up to 0 1 ma are compatible with the empirical data on h chondrite cooling histories best fit models yield excellent agreement with the cooling age data particularly they indicate that i 26 al was the major heat source driving metamorphism while 60 fe contributed rather marginally ii maximum temperatures remained below partial melting temperatures throughout the body indicating that no partial differentiation occurred on the h chondrite parent asteroid iii the h chondrite asteroid formed 2 ma after cais briefly after most ordinary chondrite chondrules formed if 26 al abundance defines a chronological sequence

episodic formation of refractory inclusions in the solar system and their presolar heritage abstract refractory inclusions ca al rich inclusions cais and amoeboid olivine aggregates aoas in primitive meteorites are the oldest solar system solids they formed in the hot inner protoplanetary disk and as such provide insights into the earliest disk dynamics and physicochemical processing of the dust and gas that accreted to form the sun and its planetary system using the short lived 26al to 26mg decay system we show that bulk refractory inclusions in cv vigarano type and cr renazzo type carbonaceous chondrites captured at least two distinct 26al rich 26al 27al ratios of 5 10 5 populations of refractory inclusions characterized by different initial 26mg 24mg isotope compositions 26mg 0 another 26al poor cai records an even larger 26mg 0 deficit this suggests that formation of refractory inclusions was punctuated and recurrent possibly associated with episodic outbursts from the accreting proto sun lasting as short as 10 myr old dust

glaciochemistry of polar ice cores a review human activities have already modified the chemical composition of the natural atmosphere even in very remote regions of the world the study of chemical parameters stored in solid precipitation and accumulated on polar ice sheets over the last several hundred thousand years provides a unique tool for obtaining information on the composition of the preindustrial atmosphere and its natural variability over the past this paper deals with the chemistry of polar ice focused on the soluble mineral na nh4 k ca mg h f cl no3 so4 and h2o2 and organic methanesulfonate ch3so3 formate hcoo acetate ch3coo and formaldehyde hcho species and their interpretation in terms of past atmospheric composition aerosols and water soluble gaseous species we discuss ice core dating the difficulties connected with trace measurements and the significance of the ionic composition of snow we examine temporal from the last decades back to the last climatic cycle and spatial including examples from coastal as well as central areas of greenland and antarctica variations in the ionic budget of the precipitation and evaluate ice core studies in terms of the chemical composition of our past atmosphere we review 1 how greenland and antarctic ice cores that span the last few centuries have provided information on the impact of human activities and 2 how the chemistry of deep ice cores provides information on various past natural phenomena such as climatic variations glacial interglacial changes el nino volcanic eruptions and large boreal forest fires

the fate of magmas in planetesimals and the retention of primitive chondritic crusts abstract high abundances of short lived radiogenic isotopes in the early solar system led to interior melting and differentiation on many of the first planetesimals petrologic isotopic and paleomagnetic evidence suggests that some differentiated planetesimals retained primitive chondritic material the preservation of a cold chondritic lid depends on whether deep melts are able to ascend and breach the chondritic crust we evaluate the likelihood of melt ascent on a range of chondritic parent bodies we find that due to the efficient ascent of free volatiles in the gas and supercritical fluid phases at temperatures still below the solidus for silicates and metals mobile silicate melts on planetesimals were likely volatile depleted by calculating the densities of such melts we show that silicate melts likely breached crusts of enstatite chondrite compositions but did not ascend in the cv and cm parent bodies ordinary chondrite melts represent an intermediate case these predictions are consistent with paleomagnetic results from cv and cm chondrites as well as spectral observations of large e type asteroids

loess in europe mass accumulation rates during the last glacial period abstract upper pleistocene loess palaeosol sequences provide excellent high resolution terrestrial archives of climate forcing due to improvements in numerical age determinations especially in luminescence dating methods a more reliable time based reconstruction of the past climate and environmental change has become available for the loess record in europe chronological information was collected from 43 sites along a northwest to southeast transect in europe thirty three of these sites had sufficient age information to allow estimation of mass accumulation rates and it was possible to isolate the mass accumulation rates of primary loess during the last glacial period 28 13 ka bp at 21 of these locations these sites fall along a coarse climatic gradient from the relatively coastal climate of belgium and france to the drier more continental climate of central europe interpreting mass accumulation rates of loess in terms of this climatic gradient is not straightforward as these deposits are dominated by sources in floodplains and large river systems thus accumulation rates are influenced strongly by regional wind and precipitation patterns but mostly by the availability of glacially derived material from the alps and the periglacial terrains that characterized european fluvial systems during and immediately following glaciation

accretion timescales and style of asteroidal differentiation in an 26al poor protoplanetary disk the decay of radioactive 26al to 26mg half life of 730 000 years is postulated to have been the main energy source promoting asteroidal melting and differentiation in the nascent solar system high resolution chronological information provided by the 26al 26mg decay system is therefore intrinsically linked to the thermal evolution of early formed planetesimals in this paper we explore the timing and style of asteroidal differentiation by combining high precision mg isotope measurements of meteorites with thermal evolution models for planetesimals in detail we report mg isotope data for a suite of olivine rich al mg 0 achondritic meteorites as well as a few chondrites main group pyroxene and the zinder pallasites as well as the lodranite all record deficits in the mass independent component of 26mg 26mg relative to chondrites and earth this isotope signal is expected for the retarded ingrowth of radiogenic 26mg in olivine rich residues produced through partial silicate melting during 26al decay and consistent with their marginally heavy mg isotope composition relative to ordinary chondrites which may reflect the early extraction of isotopically light partial melts from the source rock we propose that their parent planetesimals started forming within 250 000 years of solar system formation from a hot 500 k inner protoplanetary disk region characterized by a reduced initial 26al 27al 0 abundance 1 2 10 5 relative to the 26al 27al 0 value in cais of 5 25 10 5 this effectively reduced the total heat production and allowed for the preservation of solid residues produced through progressive silicate melting with depth within the planetesimals these non carbonaceous planetesimals acquired their mass throughout an extended period 3 myr of continuous accretion thereby generating onion shell structures of incompletely differentiated zones consisting of olivine rich residues overlaid by metachondrites and undifferentiated chondritic crusts in contrast individual olivine crystals from eagle station pallasites record variable 26mg excesses suggesting that these crystals captured the 26mg evolution of a magmatic reservoir controlled by fractional crystallization processes during the lifespan of 26al similar to previous suggestions based on isotopic evidence we suggest that eagle station pallasites formed from precursor material similar in composition to carbonaceous chondrites from a cool outer protoplanetary disk region characterized by 26al 27al 0 2 7 10 5 protracted planetesimal accretion timescales at large orbital distances with onset of accretion 0 3 1 myr post cais may have resulted in significant radiative heat loss and thus efficient early interior cooling of slowly accreting carbonaceous planetesimals

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

growth and evolution of asteroids asteroids are what is left of the precursors to the terrestrial planets they are stunning in their diversity ranging from charcoal black worlds the size of a hilltop spinning like a carnival ride to dog bone shaped metallic remnants of some cataclysmically disrupted planetary core to worlds as stately as ceres and vesta and fragments thereof to garden variety fractured and blocky nuggets that dominate near earth space asteroid belts are common around sun like stars when properly seen as unaccreted residues as scraps on the floor of the planetary bakery the diversity of asteroids can be fully appreciated for to paraphrase tolstoy accreted planets are all alike every unaccreted planet is unaccreted in its own way

revisiting the chronology and environmental conditions for the accretion of late pleistocene early holocene pampean loess argentina abstract the present research work reviews the age models of three previously studied loess sections across 700 km in the loess belt of the pampean region in central argentina the loess sections were investigated for the first time through high resolution luminescence dating in order to determine the chronology of the loess deposits and its temporal correlation with important palaeoclimatic records of the southern hemisphere reliable estimations of mass accumulation rates mars for loess were used to infer the temporal dust flux variation during the last glacial interglacial transition in southern south america the new age models have significant differences compared to the previously published ones of likely last glacial maximum lgm ages the three studied sections showed general bimodal grain size distributions consistent with multiple sources contributing dust to the pampas it is observed that higher mars values are associated with an increased presence of finer loess increases in loess accumulation are coeval with climatic transitions from wetter to drier periods in the puna altiplano plateau and high mars are related to synchronous climatic shifts to humid conditions in the pampean plain contrasting with dust fluxes observed in the more distal palaeoarchives i e the south atlantic ocean and the antarctic ice sheet the new data suggest increased dust accumulation in the pampas during the antarctic cold reversal acr and the holocene this supports the idea that changes related to atmospheric transport efficiency can better explain dust flux variations observed over glacial interglacial periods in distant palaeoarchives

carbonaceous achondrites northwest africa 6704 6693 milestones for early solar system chronology and genealogy abstract northwest africa nwa 6704 6693 are medium to coarse grained achondrites with unique petrologic and geochemical traits that are distinct from the currently established meteorite groups here we report on the extinct 26al 26mg and 53mn 53cr systems to establish fine scale chronology of its formation and cr and ti isotopic anomalies to constrain the composition of the source reservoir of nwa 6704 6693 excesses in the neutron rich 54cr and 50ti isotopes due to nucleosynthetic anomalies separate nwa 6704 6693 from the vast majority of established achondrites and instead resemble the excesses seen among the carbonaceous chondrites specifically the cr type chondrites the excesses in these isotopes indicate a common feeding zone during accretion in the protoplanetary disk between the source of nwa 6704 6693 and that of the carbonaceous chondrites the 26al 26mg data for pyroxene and plagioclase from nwa 6704 yield a 26al 27al 0 3 15 0 38 10 7 mswd 0 49 and an initial 26mg 0 004 0 005 at the time of isotopic closure this initial 26al 27al 0 translates to an absolute age of 4563 14 0 38 ma relative to the d orbigny angrite however given the potential heterogeneity of 26al the d orbigny angrite might not be a good age anchor for the purpose of calculating 26al 26mg ages the 26al 26mg age relative to another carbonaceous achondrite nwa 2976 is 4562 66 0 60 ma the 53mn 53cr systematics of nwa 6704 6693 indicate a 53mn 55mn 0 of 2 59 0 34 10 6 mswd 1 2 with an evolved initial e53cr of 0 14 0 03 the 53mn 55mn 0 yields an 53mn 53cr age of 4562 17 0 76 ma relative to the d orbigny angrite concordant ages determined using the short lived 26al 26mg and 53mn 53cr systems and extant 207pb 206pb system 4562 60 0 30 ma for nwa 6704 6693 amelin et al 2019 indicate rapid cooling and nearly contemporaneous closing of multiple isotope systems the ancient crystallization ages and positive 54cr and 50ti anomalies of nwa 6704 6693 indicate widespread melting and differentiation processes occurring in both non carbonaceous nc and carbonaceous chondrite cc regions of the protoplanetary disk additionally we report the cr and ti isotopic composition for a petrologic range of cr type materials cr2 cr6 and achondrites the additional cr and ti isotopic data for these cr type materials indicates a range in isotopic composition not previously observed based on cr2 chondrites alone

hf w thermochronometry ii accretion and thermal history of the acapulcoite lodranite parent body article acapulcoites and lodranites are highly metamorphosed to partially molten meteorites with mineral and bulk compositions similar to those of ordinary chondrites these properties place the acapulcoites and lodranites between the unmelted chondrites and the differentiated meteorites and as such acapulcoites lodranites are of special interest for understanding the initial stages of asteroid differentiation as well as the role of 26 al heating in the thermal history of asteroids to constrain the accretion timescale and thermal history of the acapulcoite lodranite parent body and to compare these results to the thermal histories of other meteorite parent bodies the hf w system was applied to several acapulcoites and lodranites acapulcoites dhofar 125 and nwa 2775 and lodranite nwa 2627 have indistinguishable hf w ages of tcai 5 2 0 9 ma and tcai 5 7 1 0 ma corresponding to absolute ages of 4563 1 0 8 ma and 4562 6 0 9 ma closure temperatures for the hf w system for acapulcoites and lodranites estimated from numerical simulations of w diffusion in high ca pyroxene are 975 50 c and 1025 50 c respectively owing to these high closure temperatures the hf w ages provide information on the earliest high temperature evolution and combined with thermal modeling indicate that the acapulcoite lodranite parent body accreted 1 5 2 ma after cai formation was internally heated by 26

a petrological and chemical reexamination of main group pallasite formation abstract the large number of pallasite parent bodies suggests that their formation was a common event in asteroid evolution new microprobe data has been generated for pallasite olivines and chromites that indicate subsolidus redox processes while literature data has been collated and correlated to form new results and interpretations the new data include information on metal compositions the metal cooling rates the formation of round and fragmental olivine the close packing of olivine the crystallization of the phosphates phosphoran olivine and orthopyroxene and the bulk pallasite p and s contents a model for main group pallasites has been developed using fractional melting of a chondritic precursor to make a multi layered parent body one portion of this contains a gradational metal olivine pallasite texture concentric downward crystallization of the molten metal is indicated based on cooling rates and metal compositions fractional crystallization of the residual silicate and metallic melts produces the minor phases on cooling comparisons to and a brief review of past models particularly those utilizing mixing have been made

did the carbonaceous chondrites evolve in the crustal regions of partially differentiated asteroids 1 carbonaceous chondrites are considered to be the most primitive meteorites that contain some of the earliest formed solar system phases e g ca al rich inclusions and chondrules the parent bodies of the carbonaceous chondrites are traditionally known to have experienced aqueous alteration however the recent paleomagnetic records of the cv chondrite allende indicate remnant magnetism that suggests that these chondrites possibly evolved on the crustal region of a partially differentiated asteroid having a convective molten iron core we present results based on our comprehensive numerical simulations of the scenario involving melting and planetary differentiation of asteroids the possibility of a sizable carbonaceous chondritic crust on these differentiated bodies is explored the simulations indicate that it could be possible to explain the paleomagnetic records of the chondrites by the dynamo generated magnetic field from the convective molten iron core apart from the slow linear accretion scenario we envisage a scenario involving two episodes of accretion of the asteroids an early rapid accretion of the asteroids in the initial stage perhaps within the initial 2 myr would produce a sizable molten iron core subsequent to differentiation to produce the required magnetic fields this would be followed by a slow accretion of consolidated chondritic crust perhaps over several million years there is also a possibility of the disrupted expulsion of the chondritic crust by the internal pressures generated by gases released during hydration dehydration reactions

numerical simulations of the differentiation of accreting planetesimals with 26al and 60fe as the heat sources numerical simulations have been performed for the differentiation of planetesimals undergoing linear accretion growth with 26al and 60fe as the heat sources planetesimal accretion was started at chosen times up to 3 ma after ca al rich inclusions cais were formed and was continued for periods of 0 001 1 ma the planetesimals were initially porous unconsolidated bodies at 250 k but became sintered at around 700 k ending up as compact bodies whose final radii were 20 50 100 or 270 km with further heating the planetesimals underwent melting and igneous differentiation two approaches to core segregation were tried in the first labelled a the core grew gradually before silicate began to melt and in the second labelled b the core segregated once the silicate had become 40 molten in a when the silicate had become 20 molten the basaltic melt fraction began migrating upward to the surface carrying 26al with it the 60fe partitioned between core and mantle the results show that the rate and timing of core and crust formation depend mainly on the time after cais when planetesimal accretion started they imply significant melting where accretion was complete before 2 ma and a little melting in the deep interiors of planetesimals that accreted as late as 3 ma the latest melting would have occurred at 10 ma the effect on core and crust formation of the planetesimals final size the duration of accretion and the choice of 60fe 56fe initial were also found to be important particularly where accretion was late the results are consistent with the isotopic ages of differentiated meteorites and they suggest that the accretion of chondritic parent bodies began more than 2 or 3 ma after cais

26 al 26 mg and 207 pb 206 pb systematics of allende cais canonical solar initial 26 al 27 al ratio reinstated abstract the precise knowledge of the initial 26 al 27 al ratio 26 al 27 al 0 is crucial if we are to use the very first solid objects formed in our solar system calcium aluminum rich inclusions cais as the time zero age anchor and guide future work with other short lived radio chronometers in the early solar system as well as determining the inventory of heat budgets from radioactivities for early planetary differentiation new high precision multi collector inductively coupled plasma mass spectrometry mc icp ms measurements of 27 al 24 mg ratios and mg isotopic compositions of nine whole rock cais six mineralogically characterized fragments and three micro drilled inclusions from the cv carbonaceous chondrite allende yield a well defined 26 al 26 mg fossil isochron with an 26 al 27 al 0 of 5 23 0 13 10 5 internal mineral isochrons obtained for three of these cais a44a ajef and a43 are consistent with the whole rock cai isochron the mineral isochron of ajef with 26 al 27 al 0 4 96 0 25 10 5 anchored to our precisely determined absolute 207 pb 206 pb age of 4567 60 0 36 ma for the same mineral separates reinstate the canonical 26 al 27 al 0 of 5 10 5 for the early solar system the uncertainty in 26 al 27 al 0 corresponds to a maximum time span of 20 ka thousand years suggesting that the allende cai formation events were culminated within this time span although all allende cais studied experienced multistage formation history including melting and evaporation in the solar nebula and post crystallization alteration likely on the asteroidal parent body the 26 al 26 mg and u pb isotopic systematics of the mineral separates and bulk cais behaved largely as closed system since their formation our data do not support the supra canonical 26 al 27 al ratio of individual minerals or their mixtures in cv cais suggesting that the supra canonical 26 al 27 al ratio in the cv cais may have resulted from post crystallization inter mineral redistribution of mg isotopes within an individual inclusion this redistribution must be volumetrically minor in order to satisfy the mass balance of the precisely defined bulk cai and bulk mineral data obtained by mc icp ms the radiogenic 208 pb 206 pb ratio obtained as a by product from the pb pb age dating is used to estimate time integrated 232 th 238 u ratio value of cais limited variations among the minerals within a single cai contrasted by much larger variations among the bulk cais suggest th u fractionation occurred prior to crystallization of igneous cais if interpreted as primordial heterogeneity the value can be used to calculate the mean age of the interstellar dust from which the cais condensed

the isotopic composition of magnesium in the inner solar system abstract we report high precision mc icpms measurements of 25 mg 24 mg and 26 mg 24 mg isotope ratios for 14 meteorites both primitive and differentiated 5 lunar basalts and breccia samples 5 terrestrial basalts 1 dunite and 3 peridotites we estimate the 26 mg value of the bulk silicate earth bse at 0 54 0 04 2se w r t dsm3 carbonaceous and ordinary chondrites show an average 26 mg of 0 52 0 04 2se martian meteorites show a narrow range in 26 mg with an average 26 mg of 0 57 0 02 2se average 26 mg of pallasite olivines is 0 54 0 04 2se whereas that of lunar samples including ilmenite basalts olivine basalt and one crystalline breccia is 0 51 0 03 2se our data demonstrate that the overall stable mg isotopic composition of the inner solar system average 25 mg 0 273 26 mg 0 535 is homogeneous to within 0 04 for 26 mg 24 mg this value is indistinguishable from that of the bse and lunar samples demonstrating that the mg isotopic composition of the earth moon system is chondritic accurate determination of the mg isotopic composition of the rocky planets is important for mg isotope studies of surface processes on earth as well as for using mg isotope data to understand evaporation and condensation effects in the solar nebula consistent with a recent report we find that clinopyroxenes have higher 26 mg than co existing olivines and orthopyroxenes in mantle peridotites although the magnitude of this difference varies 0 08 to 0 2 such small mineral fractionations along with differences between components in primitive meteorites cais chondrules and matrix preclude the resolution of mass dependent fractionation differences smaller than about 0 05 between solar system objects we demonstrate that our results do not support the recent claims that i the earth moon system has a unique mg isotope composition different from chondrites or ii the higher 26 mg values up to 0 0 reported for chondrites achondrites terrestrial basalts and peridotites to address the issue of inter laboratory discrepancies on the mg isotopic composition of silicate rocks we have prepared 3 pure mg standards with wide ranging 26 mg 3 75 to 0 69 with respect to dsm3 as well as a large volume of homogenized olivine from the san carlos peridotite which will be available to the scientific community for future comparative studies

iridium concentration as an estimation of instantaneous sediment accumulation rates ir concentrations and mass accumulation rates from nine deep sea cores one from the atlantic ocean and eight from the pacific ocean were compiled to evaluate a new technique for determining mass accumulation rates the technique is based on the large difference of the high ir abundance in extraterrestrial matter versus the low ir contents in terrestrial material assuming a constant flux of cosmic matter this difference leads to high ir concentrations in slowly accumulating sediments versus low ir concentration in rapidly accumulating sediments the method is independent of stratigraphic control and does not require knowledge of age of the deposit we note that ir concentrations in some slowly accumulating sediments are of the same order of magnitude as some of those reported for the cretaceous tertiary boundary event

a quantitative model of magnetic enhancement in loessic soils we present a quantitative model for the climatic dependence of magnetic enhancement in loessic soils the model is based on the widely accepted hypothesis that ultrafine magnetite precipitates during alternating wetting and drying cycles in the soil micropores the rate at which this occurs depends on the frequency of drying wetting cycles and on the average moisture of the soil both parameters are estimated using a statistical model for the soil water balance that depends on frequency and intensity of rainfall events and on water loss by evapotranspiration monthly climatic tables are used to calculate the average soil moisture and the rate of pedogenic magnetite production which is proportional to a new parameter called magnetite enhancement proxy mep our model is tested by comparing mep calculated for known present day climates with the magnetic enhancement of modern soils the magnetic enhancement factor defined as the ratio between a given magnetic enhancement parameter and mep is expected to be a site independent constant we show that magnetic enhancement differences between soils from the chinese loess plateau and from midwestern u s are explained by our model which yields similar magnetic enhancement factors for the two regions our model is also successful in predicting the mean annual rainfall threshold above which magnetic enhancement declines in a given type of climate

26al 26mg dating of asteroidal magmatism in the young solar system abstract we present high precision mg isotope data for most classes of basaltic meteorites including eucrites mesosiderite silicate clasts angrites and the ungrouped northwest africa nwa 2976 measured by pseudo high resolution multiple collector inductively coupled plasma mass spectrometry and utilising improved techniques for chemical purification of mg with the exception of the angrites angra dos reis lewis cliff lew 86010 nwa 1296 and nwa 2999 and the diogenite bilanga which have either been shown to have young ages by other dating techniques or have low al mg ratios all bulk samples of basaltic meteorites have 26mg excesses 26 mg 0 0135 to 0 0392 the 26mg excesses cannot be explained by analytical artefacts cosmogenic effects or heterogeneity of initial 26al 27al al mg ratios or mg isotopes in asteroidal parent bodies as compared to earth or chondrites the 26mg excesses record asteroidal melting and formation of basaltic magmas with super chondritic al mg and confirm that radioactive decay of short lived 26al was the primary heat source that melted planetesimals model 26al 26mg ages for magmatism on the eucrite mesosiderite angrite and nwa 2976 parent bodies are 2 6 3 2 3 9 4 1 and 3 5 myr respectively after formation of calcium aluminium rich inclusions cais however the validity of these model ages depends on whether the elevated al mg ratios of basaltic meteorites result from magma ocean evolution on asteroids through fractional crystallisation or directly during partial melting mineral isochrons for the angrites sahara sah 99555 and d orbigny and nwa 2976 yield ages of 5 06 0 05 0 06 myr and 4 86 0 09 0 10 myr respectively after cai formation both isochrons have elevated initial 26 mg values given the brecciated and equilibrated texture of nwa 2976 it is probable that its isochron age and elevated initial 26 mg 0 0175 0 0034 reflects thermal resetting during an impact event and slow cooling on its parent body however in the case of the angrites the marginally elevated initial 26 mg 0 0068 0 0058 may reflect either 26 mg ingrowth in a magma ocean prior to eruption and crystallisation or in an older igneous protolith with super chondritic al mg prior to impact melting and crystallisation of these angrites or partial internal re equilibration of mg isotopes after crystallisation 26al 26mg model ages and an olivine pyroxene whole rock isochron for the angrites sah 99555 and d orbigny are in good agreement with age constraints from 53mn 53cr and 182hf 182w short lived chronometers suggesting that the 26al 26mg feldspar controlled isochron ages for these angrites may be compromised by the partial resetting of feldspar mg isotope systematics even when age constraints from the 26al 26mg angrite model ages or the mafic mineral whole rock isochron are considered the relative time difference between sah 99555 d orbigny crystallisation and cai formation cannot be reconciled with pb pb ages for sah 99555 d orbigny and cais which are ca 1 0 myr too old angrites or too young cais for reasons that are not clear this discrepancy might indicate that 26al was markedly lower ca 40 in the planetesimal and planet forming regions of the proto planetary disc as compared to cais or that cai pb pb ages may not accurately date cai formation which might be better dated by the 182hf 182w and 26al 26mg chronometers as 4568 3 0 7 burkhardt et al 2008 and 4568 5 0 3 ma herein respectively when mapped onto an absolute timescale using pb pb ages for angrites

chronology of the angrite parent body and implications for core formation in protoplanets abstract angrites formed by some of the earliest igneous activity in the solar system and provide insights into the early stages of planetary melting and differentiation moreover they are pivotal reference points for early solar system chronology in order to study the processes and timescales of metal segregation in early protoplanets and to assess the distribution of short lived radionuclides in the early solar system the 182 hf 182 w system was applied to a comprehensive suite of angrites 182 hf 182 w isochron ages for angrites are in excellent agreement with previously reported 207 pb 206 pb and 53 mn 53 cr results but are 1 myr older than ages obtained from 26 al 26 mg chronometry these inconsistencies probably reflect a disturbance of the al mg system in the angrite feldspars but could alternatively be explained by a heterogeneous distribution of 26 al in the early solar system based on the hf w results four texturally and temporally resolved groups of angrites can be identified that were derived from at least two distinct mantle sources these mantle sources are the result of separate events of core formation both of which took place within 2 myr of cai formation thus core formation in the angrite parent body did not occur as a single event of metal segregation from a global magma ocean but rather took place under varying conditions by several more local events the disparate hf w systematics of the two distinct angrite source regions indicate that convection in the magma ocean was inefficient in homogenizing the composition of the mantle possibly as a result of a continuous bombardment with small planetesimals during ongoing core formation such impacts could have constantly removed primordial and earlier formed crust facilitating rapid cooling of the magma ocean which solidified as early as 3 6 0 7 myr after cai formation

si isotope systematics of meteorites and terrestrial peridotites implications for mg si fractionation in the solar nebula and for si in the earth s core abstract high precision si isotope ratios have been measured for a series of meteorites and terrestrial samples using high resolution multi collector icp ms our results differ from those reported in an earlier study georg et al 2007 si in the earth s core nature 447 1102 1106 in two important aspects first our data set reveals systematic differences in 30 si between different chondrite groups that are correlated with their mg si elemental ratio second in agreement with the previous study 30 si for the terrestrial samples are higher than values for chondrites but the difference between the bulk silicate earth bse and the carbonaceous chondrites 30 si bse c arbonaceous chondrites 0 08 0 04 1 standard deviation is about a factor of 2 smaller than previously reported the 30 si versus mg si trend defined by the chondrite groups can be explained by reaction of olivine with a sio rich vapor to form enstatite starting from a carbonaceous chondrite composition in contrast the difference between the bse and carbonaceous chondrites must reflect a different process and can be explained by incorporation of si into the earth s core during metal silicate equilibration in a deep magma ocean the observed si isotope fractionation is consistent with the temperatures and pressures of metal silicate equilibration derived from siderophile element abundances in the earth s mantle

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

characterisation of two fluvio lacustrine loessoid deposits on the island of gran canaria canary islands abstract the canary islands are close to the largest desert in the world the sahara and as a result the influence of air transported dust in the area is of great significance the present analysis consists of a study of two deposits in the ne and nw respectively of the island of gran canaria considered as fluvio lacustrine loessoids they exhibit the characteristics of aeolian deposits re worked by fluvial processes at the mouth of gullies and later edaphized in the nw profile galdar formed from 400 ka to present there are four different levels with abundant manganese stains over each and separated by dense calcrete laminations this sequence may be associated with cyclical processes of deposits in humid conditions and drying mn mobility plus the formation of arid soil carbonate precipitation the formation of the galdar profile took place between the upper pliocene and the upper pleistocene holocene the ne profile jinamar reveals a similar cyclic profile the jinamar fluvio loess deposit was formed between the upper pliocene and the upper pleistocene 1 96 0 1 ma the high percentage of the silt fraction 60 90 and the high percentage of quartz a mineral which is totally imported from the sahara desert are the main arguments in favour of the definition of these loess like deposits

lead and mg isotopic age constraints on the evolution of the hed parent body the large collection of howardite eucrite diogenite hed meteorites allows us to study the initial magmatic differentiation of a planetesimal we report pb pb ages of the unequilibrated north west africa nwa 4215 and dhofar 700 diogenite meteorites and their mass independent 26mg isotope compositions 26mg to better understand the timing of differentiation and crystallization of their source reservoir s nwa 4215 defines a pb pb age of 4484 5 7 9 myr and has a 26mg excess of 2 3 1 6 ppm whereas dhofar 700 has a pb pb age of 4546 4 4 7 myr and a 26mg excess of 25 5 1 9 ppm we interpret the young age of nwa 4215 as a thermal overprint but the age of dhofar 700 is interpreted to represent a primary crystallization age combining our new data with published mg isotope and trace element data suggests that approximately half of the diogenites for which such data are available crystallized within the first 1 2 myr of our solar system consistent with a short lived early formed magma ocean undergoing convective cooling the other half of the diogenites including both nwa 4215 and dhofar 700 are best explained by their crystallization in slowly cooled isolated magma chambers lasting over at least 20 myr

the record of continental dust from australia in tasman sea sediments abstract the flux of aeolian dust from australia to sediments of the tasman sea has increased during glacial stages of the last four glacial cycles low fluxes of dust from australia before 350 ka were followed by an increase in stage 10 and high fluxes in peak glacial periods thereafter the initiation of higher dust fluxes in stage 10 is consisten with previous estimates of the age of onset of aridity in the source area dust flux to the tasman sea is thought to record the intensity of deflation from the source area in interior southeastern australia which was marked by arid conditions and possibly greater windiness during the last glacial a transect of five cores from the central tasman sea revealed consistently low dust fluxes north of 33 s increasing southward to approximately 40 s glacial to interglacial movement of the northern boundary of the dust plume governed by the position of the subtropical ridge was less than 6 latitude probably closer to 3 350 km the position of the dust plume determined in this study and its response to climate change are significantly different from a previous reconstruction based on the measurement of quartz content of the non biogenic sediment fraction

stony iron meteorites history of the metal phase according to tungsten isotopes abstract the global composition of the early solar system is thought to be roughly chondritic in terms of refractory components and this means that metal and silicate should be present together in early planetesimals to fully understand the metal silicate differentiation process within the eucrite parent body epb it is important to try and identify the metal reservoir that is complementary to the silicate part the isotope 182 of tungsten w a siderophile element is partly formed from the decay of 182 hf and w isotopes are useful for examining metal silicate segregation the w isotopic composition expected for the metal that is complementary to eucrites falls in the range of iron meteorites however mesosiderites seem to be genetically linked to eucrites based on petrologic and oxygen isotopic similarities therefore we undertook the analysis of the metal phase of these stony irons here we present tungsten isotopic data for mesosiderite and pallasite metal to characterize their parent body bodies and to assess possible relationships with eucrites all stony iron metals are depleted in radiogenic tungsten by 1 3 to 4 2 e units relative to the terrestrial standard while chondrites for comparison are depleted by 1 9 e units in addition to w isotopic heterogeneity from one stony iron to another there is also w isotopic heterogeneity within individual meteorites a formation model is tentatively proposed where we show that mesosiderites pallasites and eucrites could possibly come from the same parent body several hypotheses are discussed to explain the isotopic heterogeneity the production of cosmogenic tungsten the in situ decay of hafnium present in inclusions and tungsten diffusion processes after metal silicate mixing during the cooling of the meteorites the two latter hypotheses provide the best explanation of our data

60fe 60ni chronology of core formation in mars abstract the timescales of accretion core formation and magmatic differentiation in planetary bodies can be constrained using extinct radionuclide systems experiments have shown that ni becomes more siderophile with decreasing pressure which is reflected in the progressively higher fe ni ratios in the mantles of earth mars and vesta mars formed rapidly and its mantle has a high fe ni ratio so the 60fe 60ni decay system t 1 2 2 62 myr is well suited to establish the timescale of core formation in this object we report new measurements of 60ni 58ni ratios in bulk snc martian shergotty nakhla chassigny meteorites and chondrites the difference in e ni 60 values between snc meteorites and the building blocks of mars assumed to be chondritic 55 ordinary chondrites 45 enstatite chondrites is 0 028 0 023 95 confidence interval using a model of growth of planetary embryo this translates into a time for mars to have reached 44 of its present size of 1 9 0 8 1 7 myr with a strict lower limit of 1 2 myr after solar system formation which agrees with a previous estimate based on 182hf 182w systematics the presence of mars when planetesimals were still being formed may have influenced the formation of chondrules through bow shocks or by inducing collisions between dynamically excited planetesimals

holocene loess sedimentation along the qilian shan china significance for understanding the processes and timing of loess deposition abstract we present optical ages for well preserved loess deposits along the qilian shan a 500 km long mountain belt forming the tectonically active northeastern margin of the tibetan plateau loess on tectonically controlled fill terraces along the shiyou and baiyong rivers was dated by applying the single aliquot regeneration sar technique to coarse grained 90 160 m quartz samples additional measurements on polymineralic fine grained 5 10 m samples were carried out to allow a comparison between various optical dating techniques currently in use the results demonstrate that i loess accumulation started between 13 and 11 ka b p continuing to the present ii mean loess accumulation rates range between 9 and 16 cm ka 1 and iii holocene loess is not restricted to certain sites only but is a prevalent phenomenon along the qilian shan mountain front the absence of loess deposits of late pleistocene age is a result of a combination of cold and dry climate conditions strong winds and the absence of a vegetation cover during the last glacial period only with the change to a warmer and moister climate at the onset of the holocene did a plant cover develop which acted as a dust trap thus initiating the formation of loess

magnesium and 54cr isotope compositions of carbonaceous chondrite chondrules insights into early disk processes we report on the petrology magnesium isotopes and mass independent 54cr 52cr compositions 54cr of 42 chondrules from cv vigarano and nwa 3118 and cr nwa 6043 nwa 801 and lap 02342 chondrites all sampled chondrules are classified as type ia or type iab have low 27al 24mg ratios 0 04 0 27 and display little or no evidence for secondary alteration processes the cv and cr chondrules show variable 25mg 24mg and 26mg 24mg values corresponding to a range of mass dependent fractionation of 500 ppm parts per million per atomic mass unit this mass dependent mg isotope fractionation is interpreted as reflecting mg isotope heterogeneity of the chondrule precursors and not the result of secondary alteration or volatility controlled processes during chondrule formation the cv and cr chondrule populations studied here are characterized by systematic deficits in the mass independent component of 26mg 26mg relative to the solar value defined by ci chondrites which we interpret as reflecting formation from precursor material with a reduced initial abundance of 26al compared to the canonical 26al 27al of 5 10 5 model initial 26al 27al values of cv and cr chondrules vary from 1 5 4 0 10 6 to 2 2 0 4 10 5 the cv chondrules display significant 54cr variability defining a range of compositions that is comparable to that observed for inner solar system primitive and differentiated meteorites in contrast cr chondrites are characterized by a narrower range of 54cr values restricted to compositions typically observed for bulk carbonaceous chondrites collectively these observations suggest that the cv chondrules formed from precursors that originated in various regions of the protoplanetary disk and were then transported to the accretion region of the cv parent asteroid whereas cr chondrule predominantly formed from precursor with carbonaceous chondrite like 54cr signatures the observed 54cr variability in chondrules from cv and cr chondrites suggest that the matrix and chondrules did not necessarily formed from the same reservoir the coupled 26mg and 54cr systematics of cr chondrules establishes that these objects formed from a thermally unprocessed and 26al poor source reservoir distinct from most inner solar system asteroids and planetary bodies possibly located beyond the orbits of the gas giants in contrast a large fraction of the cv chondrules plot on the inner solar system correlation line indicating that these objects predominantly formed from thermally processed 26al bearing precursor material akin to that of inner solar system solids asteroids and planets

magnesium isotopes constraints on the origin of mg rich olivines from the allende chondrite nebular versus planetary abstract high precision mg isotope measurements by multi collector ion microprobe show that refractory olivines from the allende chondrite either olivines isolated in the matrix 2 samples studied or olivines in type i chondrules 6 samples studied have variable 26mg enrichments and deficits calculated in permil as the 26mg deviation from the instrumental mass fractionation line relative to the earth most average 26mg noted 26mg av values between 10 and 20 analyses per chondrule are negative but the total range is from 0 029 0 010 2 sigma errors to 0 011 0 011 with an exception of one olivine at 0 043 0 023 these variations in 26mg av reflect the formation of the olivines from reservoirs enriched in various amounts of 26mg by the decay of short lived 26al t1 2 0 73 ma similarly 30 analyses of olivines from the eagle station pallasite show a 26mg av value of 0 033 0 008 as negative as some olivines from allende chondrules and the solar system initial 26mg value of 0 038 0 004 defined at the time of formation of type b ca al rich inclusions cais when 26al 27al 5 23 10 5 jacobsen et al 2008 because olivines are al poor and because their mg isotopic compositions are not reset during the chondrule forming events their 26mg av can be used to calculate model crystallization ages relative to various theoretical mg isotope growth curves the two end member scenarios considered are i a nebular growth in which the al mg ratio remains chondritic and ii a planetary growth in which a significant increase of the al mg ratio can be due to for instance olivine magmatic fractionation the low 26mg av value of olivines from the eagle station pallasite demonstrate that metal silicate differentiation occurred as early as 0 15 0 23 0 29 ma after cais in either of the growth scenarios similarly the variable 26mg av values of refractory olivines can be understood if they were formed in planetesimals which started to differentiate as early as the eagle station parent body accretion of these planetesimals must have been coeval to the formation of cais and their disruption could explain why their fragments mg rich olivines were distributed in the chondrule forming regions of the disk

pb pb chronometry and the early solar system abstract of the long lived chronometric systems only the dual decay of 238 u and 235 u to 206 pb and 207 pb respectively have appropriate half lives to resolve the ages of meteorites and their components formed in the first 5 myr of the solar system this paper reviews the theory and methods behind this chronometer offers criteria to critically evaluate pb pb ages and presents a summary of the current state and immediate future of the chronometry of the early solar system we recognize that there is some debate over the age of the solar system but conclude that an age of 4567 30 0 16 ma based on four cais dated individually by the same method in two different laboratories is presently the best constrained published value we further conclude that nebular chondrules dated by the pb pb method require that they formed contemporaneously with cais and continued to form for at least 4 myr a conclusion that implies heterogeneous distribution of the short lived 26 al nuclide in the protoplanetary disk planetesimals were already forming by 1 myr after cai formation consistent with their growth predominantly through the accretion of chondrules nebular chondrule formation was completed by 5 myr after cai formation when the impact generated cba chondrules formed after the disk was cleared of gas and dust we note that the absolute age of the solar system or any single early solar system object is not fundamental to any significant scientific question and that it is important only to know the correct relative ages of objects being used to piece together the formation history of the solar system as such we point out the risks inherent in comparing pb pb ages produced by different approaches in different laboratories at the level of the internal errors of individual ages until a cross calibration exercise using synthetic and natural standards establishes the reproducibility between laboratories only ages from a single laboratory or between laboratories having demonstrated concordance can provide a reliable relative chronometric framework for the formation and evolution of the early solar system

a study of a flowslide with significant entrainment in loess areas in china flowslides are a frequent type of natural disaster in loess areas and may result in the significant loss of properties and or casualties the dagou flowslide is a typical event in a loess area and is accompanied by significant sediment entrainment to analyze the mechanisms responsible for flowslides and to obtain the parameters for a runout analysis a field investigation was conducted specimens were sampled on site to carry out laboratory tests including a triaxial test sieve analysis and chemical component analysis the parameters were used in the runout study employing an energy based runout model an analytical entrainment model was adopted to calculate the entrainment after considering physical properties and the mechanism of the entrainment process of the loess finally the entrainment model was incorporated into the runout model to simulate the post failure process of this case energy dissipation due to the deformation of slices was considered as it was thought to be important for a slide with a significant deformation the simulation results were compared with the measurements including runout distance total volume erosion depth deposition height at different sections and velocities at specific locations the results indicate that the energy based runout model together with the entrainment model can capture the kinematic characteristics of the dagou flowslide therefore it is feasible to use this model to predict the runout characteristics of flowslides in similar areas copyright c 2017 john wiley sons ltd

partial melting and melt migration in the acapulcoite lodranite parent body we review petrologic evidence that the acapulcoites and lodranites formed by 1 vol to probably 20 vol whole rock partial melting of a chondritic precursor material at low degrees of partial melting only fe ni fes cotectic melting occurred migration distances for partial melts were short resulting in the formation of acapulcoites with essentially chondritic troilite and plagioclase contents but achondritic textures at high degrees of partial melting both fe ni fes and basaltic plagioclase pyroxene partial melts formed and the melts may have migrated out of the source rock the partial melt residues which are more or less depleted in fe ni fes and plagioclase are the lodranites melt migration was complex most acapulcoites which experienced relatively low degrees of partial melting lost little if any of the partial melt one acapulcoite lew 86220 represents a unique case in which fe ni fes and basaltic partial melts appear to have migrated from a lodranite source region into a cooler acapulcoite region where they were trapped in cases of the relatively high degrees of partial melting experienced by lodranites melts may have been partly selectively or totally removed from the rocks and fe ni fes and or basaltic partial melts may have been removed to different degrees and may in fact have been trapped on occasion in greater than chondritic proportions we model vein and dike formation and melt migration by calculating the excess pressures and vein and dike sizes for varying degrees of partial melting our calculations are broadly consistent with observations indicating that melt migration is inefficient at low degrees of partial melting and extremely efficient at high degrees of partial melting although the size of the acapulcoite lodranite parent body and the volatile contents of the chondritic precursor rocks are poorly constrained the lack of basaltic rocks in the world s meteorite collections complementary to the lodranites suggests that basaltic partial melts may have been accelerated off the body by explosive volcanism of the type envisioned by wilson and keil 1991 and ejected into space the diversity of rocks from the acapulcoite lodranite parent body may provide a basis for better understanding the diverse range of spectral subtypes recognized among the s type asteroids

provenance of dust in the pacific ocean eolian dust preserved in deep sea sediment cores provides a valuable indicator of past atmospheric circulation and continental paleoclimate in order to identify the provenance of eolian dust nd and sr isotopic compositions and rb sr and rare earth element ree concentrations have been determined for the silicate fractions of deep sea sediments from the north and central pacific ocean different regions of the pacific ocean are characterized by distinct air borne inputs producing a large range in end 10 to 1 stsr 86sr 0 705 0 721 la yb 5 15 eun eu 0 6 1 0 and sr nd 4 33 the average nd isotopic composition of pacific deep sea sediments eno 6 is more radiogenic than the average from the atlantic ena 8 in contrast the average 1475m 14and ratio for pacific sediments 0 114 is identical to that of atlantic sediments and to that of global average riverine suspended material the values of ena and 147sm 144nd are positively correlated for the pacific samples but negatively correlated for atlantic samples reflecting a fundamental difference between the dominant components in the end members with radiogenic nd island arc components in the pacific and lree enriched intraplate ocean island components in the atlantic samples from the north central pacific have distinctive unradiogenic end values of 10 87sr 86sr 0 715 high la yb 12 and low eun eu 0 6 and sr nd 3 6 these data are virtually identical to the values for loess from asia and endorse the use of these sediments as indicators of asian paleoclimate and paleowind directions island arc contributions appear to dominate in the northwest pacific resulting in higher end 1 to 1 and lower 87sr 86sr 0 705 and la yb 5 sediments from the eastern pacific tend to have intermediate sr and nd isotopic compositions but regionally variable sr nd and ree patterns they appear to be derived from the west margin of the north and south american continents rather than from asia our results confirm that dust provenance can be constrained by isotopic and geochemical analyses which will facilitate reconstructions of past atmospheric circulation and continental paleoclimate

silicon in the earth s core the earth and moon have iron isotopic abundances that are slightly heavy compared with mars the asteroid vesta and primitive meteorites the reason for this has been unclear one suggestion is that there was a large scale isotopic equilibration during the giant impact the collision between the early earth and a mars sized body that created the moon but this has seemed unlikely given that most other elements do not show the effect an analysis of 44 meteorite and terrestrial samples now shows that the silicon isotopic compositions of basaltic rocks from the earth and moon are also distinctly heavy the finding is consistent with the isotopic equilibration model and it suggests that silicon was already partitioned into the earth s core as a light element before the moon formed the silicon isotopic compositions of basaltic rocks from the earth and moon are distinctly heavy the similar isotopic composition of the bulk silicate earth and the moon are consistent with large scale isotopic equilibration during the giant impact indicating that si was already a light element in the earth s core before the moon formed small isotopic differences between the silicate minerals in planets may have developed as a result of processes associated with core formation or from evaporative losses during accretion as the planets were built up basalts from the earth and the moon do indeed appear to have iron isotopic compositions that are slightly heavy relative to those from mars vesta and primitive undifferentiated meteorites1 2 3 4 chondrites explanations for these differences have included evaporation during the giant impact that created the moon when a mars sized body collided with the young earth however lithium5 and magnesium6 lighter elements with comparable volatility7 8 9 reveal no such differences rendering evaporation unlikely as an explanation here we show that the silicon isotopic compositions of basaltic rocks from the earth and the moon are also distinctly heavy a likely cause is that silicon is one of the light elements in the earth s core we show that both the direction and magnitude of the silicon isotopic effect are in accord with current theory10 based on the stiffness of bonding in metal and silicate the similar isotopic composition of the bulk silicate earth and the moon is consistent with the recent proposal11 that there was large scale isotopic equilibration during the giant impact we conclude that si was already incorporated as a light element in the earth s core before the moon formed

late quaternary eolian deposition in central italy abstract records of eolian quartz from two continuous sediment sequences drilled in lagaccione and lago di vico volcanic lakes in central italy contribute to the knowledge of eolian deposition in the central mediterranean during the last 100 000 years the chronology is based on 14 c and 40 ar 39 ar dating and tephra analysis pollen data provide the paleoenvironmental framework and enable correlation between the cores eolian inputs were high during the steppe phases corresponding to oxygen isotope stages 4 and 2 low inputs correspond to the forest phases of the last interglacial and the middle holocene eolian inputs have increased in the late holocene patterns of eolian deposition in central italy resemble the antarctic dust record from the vostok ice core the italian patterns may also correspond with hydrological changes registered in north africa the main source of dust loading over the mediterranean now north africa may have played an important role in dust supply throughout the last climatic cycle

atmospheric summer circulation and coastal upwelling in the arabian sea during the holocene and the last glaciation accumulation rates of biogenic and lithogenic components were studied in 39 turbidite free well dated sediment cores from the northern indian ocean to define the proportions of fluvial and eolian input and to reconstruct quaternary patterns of coastal upwelling the majority of dust deposited in the western arabian sea during the holocene about 100 106 t yr 1 is advected from arabia by northwesterly winds which overlie the low level southwest monsoon the glacial increase in dust flux to 160 106 t yr 1 culminated in the northern arabian sea most probably due to i entrainment of dust rich in chlorite dolomite and lithogenic carbonate in the then dry persian gulf and ii a southward shift of the mean position of the southwest monsoon during glacial summer this shift is recorded in reduced accumulation rates of biogenic opal and increased rates of marine carbonate off somalia and oman both the terrigenous and biogenic sediment records show that the northwesterly winds and the southwest monsoon persisted over the last 27 000 yr as well as the asian continental summer heat low however the glacial seasonal time span of the southwest monsoon season was much reduced most likely because of a delay in the seasonal onset of the southwest monsoon

main group pallasites thermal history relationship to iiiab irons and origin we have determined metallographic cooling rates below 975 k for eight main group mg pallasites from ni profiles across taenite lamellae of known crystallographic orientation in metallic regions with widmanstatten patterns comparison with profiles generated by modeling kamacite growth gave cooling rates ranging from 2 5 to 18 k myr relative cooling rates were also inferred from the sizes of cloudy zone particles in 28 mg pallasites 86 170 nm and tetrataenite bandwidths in 20 mg pallasites 1050 2170 nm as these parameters are positively correlated with each other and negatively correlated with the metallographic cooling rates these three different techniques show that mg pallasites cooled below 975 k at significantly diverse rates since samples from the core mantle boundary should have indistinguishable cooling rates mg pallasites could not have cooled at this location group iiiab irons which were previously thought to be core samples from the mg pallasite body have faster cooling rates 50 350 k myr and smaller cloudy zone particle sizes and tetrataenite bandwidths this shows that iiiab irons cooled faster than mg pallasites and could not plausibly be from the same body the absence of related iron meteorites and achondrites and our thermal constraints suggest that mg pallasites cooled at diverse depths in a pallasitic body consisting of well mixed olivine and metallic fe ni such a body may have formed during an impact on a differentiated asteroid or protoplanet that mixed olivine mantle fragments with residual ir poor molten metal from the out ermost part of a core that chemically resembled the iiiab core and was 80 fractionally crystallized separation of the solid core and most of the associated mantle may have resulted from a grazing hit and run impact with a larger protoplanet or asteroid thermal calculations suggest that the radius of the pallasitic body was 400 km but the likely presence of a regolith would reduce this estimate considerably 2010 elsevier ltd all rights reserved

manganese chromium isotope systematics of carbonaceous chondrites abstract in this article we present the results of cr isotope investigations of different types of carbonaceous chondrites and of the pallasite eagle station the 53 cr 52 cr ratios in the bulk samples of carbonaceous chondrites are correlated with 55 mn 52 cr ratios the slope of the correlation line yields a 53 mn 55 mn ratio of 8 5 1 5 10 6 at the time of mn cr fractionation mapping this ratio onto an absolute time scale yields a time for this event of 4568 1 0 8 1 1 ma ago this time is very similar to the formation age of efremovka cais of 4567 2 0 6 ma y amelin a n krot i d hutcheon a a ulyanov lead isotopic ages of chondrules and calcium aluminum rich inclusions science 297 2002 1678 1683 to a time of the chondrule formation of 4568 1 ma ago l e nyquist d lindstrom d mittlefehldt c y shih h wiesmann s wentworth r martinez manganese chromium formation intervals for chondrules from the bishunpur and chainpur meteorites meteorit planet sci 36 2001 911 938 which most likely constrains early global high temperature mn cr fractionation in a nebular setting the bulk samples of carbonaceous chondrites exhibit clear 54 cr excesses 54 cr that are correlated with the 53 cr excesses 53 cr and also with mn cr ratios one possible explanation of this correlation is that 54 cr is also radiogenic like 53 cr and was formed by the decay of the short lived parent radionuclide 54 mn the very short half life of 54 mn of 312 days would require that both short lived radionuclides 53 mn and 54 mn were generated locally in spallation reactions during the early period of an active sun the alternative and possibly more plausible explanation is the heterogeneous addition of presolar material the presolar component enriched in 54 cr is mostly contained in the matrix of carbonaceous chondrites the relative amount of matrix decreases in the sequence ci cm co cv a large proportion of mn is associated with the matrix while cr preferentially resides in the chondrules thus the mn cr ratio also follows the sequence ci cm co cv and is correlated with 54 cr the acid resistant residues of carbonaceous chondrites are characterized by relatively large excesses of 54 cr and moderate deficits of 53 cr the magnitude of these excesses and deficits decreases in the sequence ci cm cv and may imply that cr in the cm and cv residues is increasingly more equilibrated with cr from the rest of the meteorites the 53 cr 52 cr and 54 cr 52 cr ratios in the residues are anti correlated indicating that there are at least two cr components of possibly presolar origin all residues have large excesses of the most neutron rich ti isotope 50 ti the pattern of 50 ti does not exactly follow that observed for 54 cr but it is generally similar the cr isotope systematic of the pallasite eagle station indicates that the precursor of this meteorite was a cv type material the 53 mn 53 cr system indicates that the cr isotopes equilibrated in this meteorite 4557 5 0 6 ma ago

combined irsl osl single aliquot regeneration sar equivalent dose de estimates from source proximal chinese loess tectono sedimentary systems are readily recognized in northeastern tibet and elsewhere but they have proved difficult to date via conventional absolute dating techniques in the qilian shan the application of cosmogenic methods is complicated by the presence of terrace blanketing loess deposits we have chosen to explore the potential of applying optical dating techniques to directly date the loess cover deposits to provide minimum ages for terrace abandonment events we focussed on a suite of six loess mantled terraces cut into an abandoned alluvial fan sequence which was uplifted by thrust faulting on the zhangye thrust fault east of the hei he river at its exit from the qilian shan application of single aliquot regeneration sar optical dating techniques provides a chronology of terrace age we employ a double sar procedure in which aliquots are subjected to both infrared lin 830 nm and blue lin 470 nm stimulation and two sets of de determinations are produced and assumed to relate predominantly to feldspathic and quartz fine grain populations respectively our de and age determinations are stratigraphically sensible and we do not observe a significant difference between irsland osl de estimates which has been the case in previous studies r 2003 published by elsevier science ltd

mineral magnetic characterization of the upper pleniglacial nussloch loess sequence germany an insight into local environmental processes 1 first comprehensive environmental magnetism study of the nussloch rhine river valley germany loess palaeosol deposit 2 bulk ferrimagnetic concentration parameters are dominantly controlled by variations in coarse grained md ferrimagnetic particles of detrital aeolian origin 3 the imprint of waterlogging induced redoxomorphic processes on the magnetic record is observed by dissolution of fine grained magnetic minerals 4 the interpretation of magnetic susceptibility variations alone within loess and palaeosol deposits following the wind vigour or pedogenic enhancement models will be hindered by waterlogging induced redoxomorphic processes if present s u m m a r y presently most loess palaeosol magnetic susceptibility records are interpreted as following either the wind vigour model or the pedogenic enhancement model however redoxomorphic processes induced by waterlogging often referred to gleying in the loess literature are also known to alter loess deposits but their impact on loess palaeosol magnetic susceptibility records has received little attention the reported rock magnetic study aims to characterize the mineral magnetic response of loess to waterlogging induced redoxomorphic processes thus improving our understanding of mineral magnetic changes within loess deposits with respect to environmental and climate conditions the nussloch loess palaeosol deposit rhine valley germany was targeted because it is one of the best studied pleniglacial deposits for western europe in which numerous tundra gley intervals have been identified moreover a comprehensive high resolution environmental magnetism study has never been undertaken for this site various rock magnetism experiments were conducted at both room and low temperatures to characterise the composition concentration and relative magnetic grain size of the mineral magnetic assemblage the relative changes in magnetic parameters within the investigated loess interval are primarily controlled by 1 varying concentrations of coarse grained ferri magnetic particles of detrital aeolian origin and 2 dissolution of fine grained ferrimagnetic particles related to in situ post depositional alteration promoted by waterlogging induced re doxomorphic processes goethite is found to be ubiquitous throughout the studied interval and is argued to have both a primary aeolian and secondary in situ origin we conclude that redoxomorphic processes induced by waterlogging if present will hinder the interpretation of magnetic susceptibility variations within loess and palaeosol deposits following the expected relationships dictated by the wind vigour and the pedogenic enhancement magnetism models

reassessing the origin and chronology of the unique achondrite asuka 881394 implications for distribution of 26al in the early solar system abstract the achondrite asuka 881394 has mineralogy broadly similar to that of eucrites but is isotopically chemically and texturally distinct from them previous u pb chronology shows that it is very old forming within the first 0 8 ma of the formation of calcium aluminum rich inclusions cais however the age difference between asuka 881394 and other very old solar system materials cais quenched angrites measured with the 26al 26mg and 53mn 53cr extinct radionuclide chronometers and 207pb 206pb chronometer is not the same this could be interpreted to reflect heterogeneity in the distribution of 26al and 53mn in the early solar system given the significant implications for the early solar system chronology if 26al and 53mn are indeed heterogeneously distributed in this study we further investigate the origin of asuka 881394 and the apparent age discordance between short lived and absolute chronometers by focusing on measurement of its e54cr composition renewed measurements of the absolute pb pb age and new high precision measurements of its 26al 26mg systematics new cr isotope data places additional constraints on the origin of asuka 881394 its e 54cr value of 0 37 0 10e is resolvable outside of uncertainty from hed meteorites 0 72 0 10e reinforcing evidence from oxygen isotopic analyses that suggest it originated from a distinct parent body unlikely to be 4 vesta new pb pb analyses combined with using a directly measured 238u 235u ratio for age calculation result in a recalculated pb pb age of 4564 95 0 53 ma 1 5 ma younger than the previously reported age with this age asuka 881394 remains one of the oldest known achondrites in our solar system new high precision 26al 26mg data produce an initial 26al 27al ratio of 1 48 0 12 10 6 within error of previous data this ratio corresponds to an al mg age of 4563 69 0 36 ma or 4564 83 0 21 ma relative to cais and the d orbigny angrite respectively thus depending on which age anchor is used the 26al 26mg age is either 1 26 ma or 0 12 ma younger than the new pb pb age the latter being unresolved within analytical uncertainty though a potential age discrepancy between 26al 26mg and pb pb could be a result of heterogeneous distribution of 26al we demonstrate with our new high precision mg isotope data in conjunction with petrographic evidence that the mg isotope system has been disturbed in asuka 881394 we suggest that the 26al 26mg system closed to diffusion after the u pb system either due to slow cooling on the parent body or low grade metamorphic re equilibration of mg thus we can satisfactorily explain the observed age discrepancy between 26al 26mg and u pb systems in asuka 881394 without invoking heterogeneous distribution of 26al 27al ratio in the early solar system comparison of the asuka 881394 data with that of other anomalous achondrites from distinct parent bodies suggests that these could also have evolved from a source region with a canonical 26al 27al ratio because these achondrites have significant differences in their e54cr 17o systematics which could be indicative of location within the early protoplanetary disk it is consistent with homogeneous distribution of 26al in the early solar system angrites remain an outlier either because they evolved from a source with a lower 26al 27al ratio or because their 26al 26mg or pb pb data are problematic in either case this suggests that basaltic angrites are questionable as the age anchor for the entire solar system as a whole and other very old well preserved achondrites should be considered for that role

an experimental assessment of the potential of sulfide saturation of the source regions of eucrites and angrites implications for asteroidal models of core formation late accretion and volatile element depletions abstract the geochemistry of asteroidal magmas provides fundamental clues to the processes involved in the origin and early evolution of planetary bodies although sulfides are important reservoirs for a diverse suite of major and trace elements it is currently unclear whether the interiors of asteroid vesta and the angrite parent body were sulfide liquid saturated during petrogenesis of non cumulate eucrites and volcanic angrites to assess the potential of sulfide liquid saturation in the interiors of these bodies high pressure p temperature t experiments were used to quantify the sulfur concentrations at sulfide saturation scss for volcanic angrites and non cumulate eucrites the sulfide silicate partitioning behavior of various trace elements was simultaneously quantified to study their geochemical behavior at sulfide liquid saturation it was found that the measured scss values agree well with the scss values predicted from a previous thermodynamic model for high feo melts to assess the possibility of sulfide liquid saturation of the source regions of non cumulate eucrites and angrites their s abundances were compared with the calculated scss values for their source regions results show that if eucritic and angritic source regions were saturated with fes liquid significant degassing 50 80 of s must have occurred during or following their magmatic emplacement such loss is inconsistent with the s cl zn and rb isotopic compositions of non cumulate eucrites sulfide liquid saturation of eucrite and angrite source regions is also excluded from the strongly incompatible behavior of cu and hse in non cumulate eucrites and angrites riches et al 2012 additional calculations were performed to further explore the timing and extent of s loss during crystallization of the vestan magma ocean the assumption of chondritic bulk s abundances of bulk vesta would correspond with extremely high s contents of the eucrite source region s even after consideration of depletion of s due to core formation in light of the s cl zn and rb stable isotopic compositions of eucrites the s abundances in eucrites are most consistent with the hypothesis that the vestan mantle was already strongly depleted in s 70 80 by the time of vestan magma ocean crystallization resulting in more realistic s contents of the eucrite source region s the depletion of s could have been established during initial accretion of vesta or it could simply reflect accretion of volatile depleted components that experienced incomplete condensation wu et al 2018 modeling of the new experimentally determined sulfide silicate partition coefficients and previously reported vestan mantle depletions of the various chalcophile and siderophile elements suggests that sulfide liquid segregation during early vestan magma ocean crystallization is also unlikely the lack of sulfide liquid saturation in the source regions of non cumulate eucrites and angrites as well as during early vestan magma ocean solidification shows that current geochemical models of core formation and late accretion remain valid for these bodies

origin of the pluto charon system constraints from the new horizons flyby abstract new horizon s accurate determination of the sizes and densities of pluto and charon now permit precise internal models of both bodies to be constructed assuming differentiated rock ice structures we find that pluto is close to 2 3 solar composition anhydrous rock by mass and charon 3 5 solar composition anhydrous rock by mass pluto and charon are closer to each other in density than to other large 1000 km diameter kuiper belt bodies despite this we show that neither the possible presence of an ocean under pluto s water ice shell and no ocean within charon nor enhanced porosity at depth in charon s icy crust compared with that of pluto are sufficient to make pluto and charon s rock mass fractions match all four small satellites styx nix kerberos hydra appear much icier in comparison with either pluto or charon in terms of a giant impact origin both these inferences are most consistent with the relatively slow collision of partly differentiated precursor bodies canup astrophys j 141 35 2011 this is in turn consistent with dynamical conditions in the ancestral kuiper belt but implies that the impact precursors themselves accreted relatively late and slowly to limit 26 al and accretional heating the iciness of the small satellites is not consistent with direct formation of the pluto charon system from a streaming instability in the solar nebula followed by prompt collapse of gravitationally bound pebble piles a proposed formation mechanism for kuiper belt binaries nesvorn et al astron j 140 785 793 2010 growth of pluto scale bodies by accretion of pebbles in the ancestral kuiper belt is not ruled out however and may be needed to prevent the precursor bodies from fully differentiating due to buried accretional heat prior to the charon forming impact

lead isotope evidence for a young formation age of the earth moon system abstract a model of a giant impact between two planetary bodies is widely accepted to account for the earth moon system despite the importance of this event for understanding early earth evolution and the inventory of earth s volatiles critical to life the timing of the impact is poorly constrained we explore a data based two stage pb isotope evolution model in which the timing of the loss of volatile pb relative to refractory u in the aftermath of the giant impact is faithfully recorded in the pb isotopes of bulk silicate earth constraining the first stage pb isotopic evolution permits calculating an age range of 4 426 4 417 ga for the inflection in the u pb ratio related to the giant impact this model is supported by pb isotope data for angrite meteorites that we use to demonstrate volatility driven planetary scale pb loss was an efficient process during the early solar system the revised age is 100 myr younger than most current estimates for the age of the moon but fully consistent with recent ages for lunar ferroan anorthosite and the timing of earth s first crust inferred from the terrestrial zircon record the estimated loss of 98 of terrestrial pb relative to the solar system bulk composition by the end of the moon forming process implies that the current inventory of earth s most volatile elements including water arrived during post impact veneering by volatile rich bodies

evaluation of osmium isotopes and iridium as paleoflux tracers in pelagic carbonates new osmium os isotope and platinum group element pge concentration data are used in conjunction with published 3 he and th isotope data to determine the relative proportions of lithogenic extraterrestrial and hydrogenous iridium ir in a pacific pelagic carbonate sequence from the ocean drilling program odp site 806 on the ontong java plateau ojp these calculations demonstrate that lithogenic and extraterrestrial contributions to sedimentary ir budget are minor while hydrogenous ir accounts for roughly 85 of the total ir application of analogous partitioning calculations to previously reported data from a north pacific red clay sequence ll44gpc3 yields very similar results total ir burial fluxes at site 806 and ll44 gpc3 are also similar 45 and 30 pg cm 2 kyr 1 respectively average ir 3 he and ir xs 230 thinitial ratios calculated from the entire site 806 data set are similar to those reported earlier for pacific sites in general down core profiles of ir 3 he and xs 230 thinitial are not well correlated with one another however all three data sets show similar variance and yield sediment mass accumulation rate estimates that agree within a factor of two while these results indicate that ir concentration has potential as a point paleoflux tracer in pelagic carbonates ir based paleoflux estimates are likely subject to uncertainties that are similar to those associated with co based paleoflux estimates consequently local calibration of ir flux in space and time will be required to fully assess the potential of ir as a point paleoflux tracer measured 187 os 188 os of the ojp sediments are systematically lower than the inferred 187 os 188 os of contemporaneous seawater and a clear glacial interglacial 187 os 188 os variation is lacking mixing calculations suggest os contributions from lithogenic sources are insufficient to explain the observed 187 os 188 os variations the difference between the 187 os 188 os of bulk sediment and that of seawater is interpreted in terms of subtle contributions of unradiogenic os carried by particulate extraterrestrial material down core variations of 187 os 188 os with pt ir and os ir also point to contributions from extraterrestrial particles mixing calculations for each set of several triplicate analyses suggest that the unradiogenic os end member cannot be characterized by primary extraterrestrial particles of chondritic composition it is noteworthy that in efforts aimed at determining the effect of extraterrestrial contributions 187 os 188 os of pelagic carbonates has greater potential compared to abundances of pge an attempt has been made for the first time to estimate sediment mass accumulation rates based on amount of extraterrestrial os in the ojp samples and previously reported extraterrestrial os flux throughout most of the ojp record os isotope based paleoflux estimates are within a factor of two of those derived using other constant flux tracers meaningful flux estimates cannot be made during glacial maxima because the ojp sediments do not record the low 187 os 188 os reported previously we speculate that this discrepancy may be related to focusing of extraterrestrial particles at the ojp as has been suggested to explain down core 3 he variations

well resolved variations in the formation ages for ca al rich inclusions in the early solar system recent whole rock magnesium isotopic data for calcium aluminum rich inclusions cais in chondrite meteorites indicate that the primary nebular fractionation of aluminum from magnesium probably by condensation occurred within 20 000 years at 4 567 ga however high precision multicollector ion microprobe data for diverse cais from vigarano cv3 yield internal isochrons with a clearly resolved spread in initial 26al 27al meaning that cais formed and were reprocessed over a much longer time span primitive unmelted cais have a consistent value of 5 2 0 1 10 5 melted cais range from 5 17 10 5 to 4 24 10 5 and one single object with a complex multistage history has an internal range of 26al 27al 4 77 2 77 10 5 the entire range corresponds to an age span of 0 7 ma thus not all cais formed at time zero and only the most primitive cais should be used as benchmarks for earliest solar system chronology

holocene late pleistocene climatic ice core records from qinghai tibetan plateau three ice cores to bedrock from the dunde ice cap on the north central qinghai tibetan plateau of china provide a detailed record of holocene and wisconsin wurm late glacial stage lgs climate changes in the subtropics the records reveal that lgs conditions were apparently colder wetter and dustier than holocene conditions the lgs part of the cores is characterized by more negative 18 o ratios increased dust content decreased soluble aerosol concentrations and reduced ice crystal sizes than the holocene part these changes occurred rapidly 10 000 years ago in addition the last 60 years were apparently one of the warmest periods in the entire record equalling levels of the holocene maximum between 6000 and 8000 years ago

magnesium isotopic fractionation in chondrules from the murchison and murray cm2 carbonaceous chondrites we present high precision measurements of the mg isotopic compositions of a suite of types i and ii chondrules separated from the murchison and murray cm2 carbonaceous chondrites these chondrules are olivine and pyroxene rich and have low 27 al 24 mg ratios 0 012 0 316 the mg isotopic compositions of murray chondrules are on average lighter d 26 mg ranging from 0 95 to 0 15 relative to the dsm 3 standard than those of murchison d 26 mg ranging from 1 27 to 0 77 taken together the cm2 chondrules exhibit a narrower range of mg isotopic compositions than those from cv and cb chondrites studied previously the least altered cm2 chondrules are on average lighter average d 26 mg 0 39 0 30 2se than the moderately to heavily altered cm2 chondrules average d 26 mg 0 11 0 21 2se the compositions of cm2 chondrules are consistent with isotopic fractionation toward heavy mg being associated with the formation of secondary silicate phases on the cm2 parent body but were also probably affected by volatilization and recondensation processes involved in their original formation the low al cm2 chondrules analyzed here do not exhibit any mass independent variations in 26 mg from the decay of 26 al with the exception of two chondrules that show only small variations just outside of the analytical error in the case of the chondrule with the highest al mg ratio a type iab chondrule from murchison the lack of resolvable 26 mg excess suggests that it either formed 1 ma after calcium aluminum rich inclusions or that its al mg isotope systematics were reset by secondary alteration processes on the cm2 chondrite parent body after the decay of 26 al

aeolian sediments in the quaternary record an introduction abstract investigation of aeolian successions is providing insight into quaternary changes at the land atmosphere interface this is proving to be a valuable source of information not only on shifting desert margins but on changes of global extent recent work on the thick loess paleosol sequences of central and eastern asia has established them as sensitive indicators of changes in the semi arid sub humid zone that provide a key to changes in the global circulation some sequences in western china promise climate proxy data approaching in resolution that of recent ice core records questions considered include the provenance of loess particles the resolution and sensitivity of the aeolian record including granulometry magnetic properties and degree of palaeosol development luminescence dating and aminostratigraphy of loess and sands and the problem of inter regional correlation of the aeolian accumulation record in china and tadjikistan examples of the aeolian quaternary record are presented from north and south america europe and asia

acapulco and lodran like achondrites petrology geochemistry chronology and origin we have performed petrologic and geochemical studies of five primitive achondrites alha81187 and alha81261 acapulco like eet 84302 transitional but acapulco like and lew 88280 and mac 88177 lodran like we have also performed 39ar 40ar chronology on alha81187 alha81261 and eet 84302 lew 88280 and mac 88177 contain more ferroan olivines orthopyroxenes clinopyroxenes and chromites than do the acapulco like achondrites plagioclase is present in only alha81187 alha81261 and eet 84302 its composition does not track that of the mafic silicates eet 84302 with the most calcic plagioclase contains olivine and pyroxene with an mg intermediate between alha81187 and alha81261 similarly spinels in eet 84302 have the same mg as those in alha81187 while pyroxenes in the former are more ferroan than in the latter acapulco like achondrites have sm sc ratios between 0 8 1 5 times h chondrites and na sc ratios are between 0 81 0 times h chondrites indicating that silicate partial melts have not been lost from these rocks siderophile and chalcophile elements are fractionated and show a trend of increasing ir ni ratios with decreasing se co ratios this variation is consistent with fractionation by partial melting in the fe ni s system eet 84302 is very depleted in se and troilite is a accessory phase indicating essentially total loss of the low temperature fe ni s melt in contrast the lodran like achondrites are depleted in the highly incompatible lithophile elements relative to more compatible elements sm sc ratios are 0 2 0 7 times and na sc ratios are 0 04 0 18 times h chondrites these data are consistent with a model for formation of the lodran like achondrites as partial melting residues however the low ir ni and high se co ratios in two lodran like achondrites suggest the metal troilite in these rocks is dominated by the low melting fraction in the fe ni s system this metal troilite was added to the silicates after partial melting depleted them in a basaltic fraction the ar ar release spectra yield good plateau ages of 4 507 0 024 ga alha81187 4 511 0 007 ga alha81261 and 4 519 0 017 ga eet 84302 in good agreement with previously determined ar ar ages for other acapulco like achondrites together the ar ar ages demonstrate that metamorphism on the acapulco lodran parent body occurred 4 51 0 02 ga ago roughly 50 ma after its formation the geochemical and petrologic evidence on the acapulco and lodran like achondrites suggest that heating on the parent body was localized and heterogeneous in space and time the parent body was probably not subjected to parent body wide magmatism in contrast to the case for 4 vesta and the hed meteorites

a thermal model for the differentiation of asteroid 4 vesta based on radiogenic heating a finite element code has been developed to model the thermal history of asteroid 4 vesta this is the first attempt to model the thermal history of a differentiated asteroid through core and crust formation and subsequent cooling until geochemical closure is attained the results of the simulation are consistent with chronological measurements and other constraints provided by cumulate and noncumulate eucrites believed to have been derived from vesta the work solves two major problems with the hypothesis of heating by decay of26al an extinct radionuclide postulated to be a plausible heat source in the early solar system first the model demonstrates that it is possible to keep the mantle of vesta hot for 100 ma thereby explaining the observed difference in ages between cumulate and noncumulate eucrites second the simulation offers a possible explanation of why detectable excesses of26mg the decay product of26al are not observed in noncumulate eucrites the simulation draws a model chronology of vesta and predicts times relative to cai formation for accretion at 2 85 myr core formation at 4 58 myr crust formation at 6 58 myr and geochemical closure at 100 myr for a h chondrite asteroidal bulk composition decay of60fe is found to cause no perceptible difference in the thermal history of vesta even when sequestered into a central core although chondritic xenoliths have not been described in hed igneous lithologies the thermal model suggests the possibility that a veneer of unmelted near surface material should remain

hiatuses on voring plateau sedimentary gaps or preservation artifacts the sediments recovered on odp leg 104 have been reported to be characterized by hiatuses the hiatuses were defined by biostratigraphy and were believed to be caused by erosion related to temporary changes of bottom current composition and velocity they have been associated with major paleoenvironmental changes reorganization of global deep water production and increased bottom water flows because of the importance of hiatuses for ongoing research we decided to closely investigate the sedimentation history for the most significant pliocene and miocene biostratigraphic hiatuses by sedimentologic and geochemical means the sedimentologic studies include clay mineral distributions grain size data and organic carbon concentrations the geochemical studies include determination of full size image 1 k sr ratios 10be and ir concentrations the results of the sedimentologic studies suggest either that paleoenvironmental changes associated with hiatuses are not represented in the preserved sediments or that the hiatuses are an artifact of interpretation of the biostratigraphic data strontium isotopes indicate continuous sedimentation for the interval investigated at site 642 an interpretation confirmed by the steady decline in 10be full size image 1 k sr ratios in the interval from above and below proposed hiatuses h full size image 1 k and full size image 1 k at site 643 display stronger changes with depth than expected by steady sedimentation ir data for this same interval indicate reduced sedimentation rates combining both sedimentologic and geochemical evidence the proposed hiatuses could not be confirmed and may represent preservation artifacts

evidence for a dynamo in the main group pallasite parent body understanding the origin of pallasites stony iron meteorites made mainly of olivine crystals and feni metal has been a vexing problem since their discovery here we show that pallasite olivines host minute magnetic inclusions that have favorable magnetic recording properties our paleointensity measurements indicate strong paleomagnetic fields suggesting dynamo action in the pallasite parent body we use these data and thermal modeling to suggest that some pallasites formed when liquid feni from the core of an impactor was injected as dikes into the shallow mantle of a 200 kilometer radius protoplanet the protoplanet remained intact for at least several tens of millions of years after the olivine metal mixing event

chondrites as samples of differentiated planetesimals abstract chondritic meteorites are unmelted and variably metamorphosed aggregates of the earliest solids of the solar system the variety of metamorphic textures in chondrites motivated the onion shell model in which chondrites originated at varying depths within a parent body heated primarily by the short lived radioisotope 26 al with the highest metamorphic grade originating nearest the center allende and a few other chondrites possess a unidirectional magnetization that can be best explained by a core dynamo on their parent body indicating internal melting and differentiation here we show that a parent body that accreted to 200 km in radius by 1 5 ma after the formation of calcium aluminum rich inclusions cais would have a differentiated interior and ongoing accretion would add a solid undifferentiated crust overlying a differentiated interior consistent with formational and evolutionary constraints inferred for the cv parent body this body could have produced a magnetic field lasting more than 10 ma this hypothesis represents a new model for the origin of some chondrites presenting them as the unprocessed crusts of internally differentiated early planetesimals such bodies may exist in the asteroid belt today the shapes and masses of the two largest asteroids 1 ceres and 2 pallas can be consistent with differentiated interiors conceivably with small iron cores with hydrated silicate or ice silicate mantles covered with undifferentiated crusts

changes in continental and sea salt atmospheric loadings in central greenland during the most recent deglaciation model based estimates by fitting a very simple atmospheric impurity model to high resolution data on ice accumulation and contaminant fluxes in the gisp2 ice core we have estimated changes in the atmospheric concentrations of soluble major ions insoluble particulates and 10 be during the transition from glacial to holocene conditions for many species changes in concentration in the ice typically overestimate atmospheric changes and changes in flux to the ice typically underestimate atmospheric changes because times of increased atmospheric contaminant loading are also times of reduced snowfall the model interpolates between the flux and concentration records by explicitly allowing for wet and dry deposition processes compared to the warm preboreal that followed we estimate that the atmosphere over greenland sampled by snow accumulated during the younger dry as cold event contained on average four seven times the insoluble particulates and nearly seven times the soluble calcium derived from continental sources and about three times the sea salt but only slightly more cosmogenic 10 be

grain size distribution and depositional processes of the mineral component of abyssal sediments lessons from the north pacific grain size analyses of the mineral component of abyssal pacific surface sediments show two distinctly different size distributions that can be associated with sediments that are dominantly eolian and dominantly hemipelagic respectively in the range of 1 to 30 m eolian grains show a distinct size mode at about 2 m 9 and little material coarser than about 16 m 6 hemipelagic grains are characterized by a much flatter size distribution that has a broad size mode near 2 m 9 and important amounts of material coarser than 16 m 6 this ability to distinguish between hemipelagic and eolian grains will obviate some long standing concerns in the interpretation of deep sea sediments examples of the utility of this technique are given for the north pacific and south atlantic

u pb ages of angrites abstract precise u pb ages determined with double spike 202 pb 205 pb thermal ionization m1ass spectrometry are reported for angrites angra dos reis ador lewis cliff 86010 lew and d orbigny nineteen of 23 acid washed pyroxene fractions from these meteorites and whole rock fractions from d orbigny contain between 0 5 and 1 3 pg of total common pb indistinguishable from analytical blank measured 206 pb 204 pb ratios in these fractions are between 6300 and 14 100 for ador 1160 4500 for lew and 608 8500 for d orbigny blank corrected 206 pb 204 pb ratios for all three meteorites vary from 2160 to over 100 000 these fractions yielded precise and reproducible 207 pb 206 pb dates with the average values of 4557 65 0 13 ma for ador 4558 55 0 15 ma for lew and 4564 42 0 12 ma for d orbigny pb pb isochrons including data with slightly elevated common pb and u pb upper concordia intercepts yield similar dates the implications of these new pb isotopic ages of angrites are threefold first they demonstrate that ador and lew are not coeval and the group of slowly cooled angrites is therefore genetically diverse second the new age of lew suggests an upward revision of 53 mn 53 cr absolute ages by 0 7 ma third a precise age of d orbigny allows consistent linking of the 53 mn 53 cr and 26 al 26 mg extinct nuclide chronometers to the absolute lime scale

old formation ages of igneous clasts on the l chondrite parent body reflect an early generation of planetesimals or chondrule formation abstract the barwell meteorite contains large abundant clasts that are igneous in nature we report iodine xenon ages of five clasts and one sample of host chondrite material the fragment of host chondrite material yielded the oldest age determined 4567 8 1 2 ma two clasts produced old well defined ages of 4564 96 0 33 ma and 4565 60 0 33 ma these and a third clast having a less precise old age of 4566 0 3 2 ma are interpreted as recording the timing of crystallisation of the samples they were incorporated into the barwell parent body before it underwent thermal metamorphism but the i xe ages survived secondary processing on the parent body and were not reset by metamorphism metasomatism or shock two further clasts record younger ages of 4560 96 0 45 ma and 4554 22 0 38 ma these samples contain a high abundance of albitic mesostasis and the most likely explanation of the ages is that they record the timing of metasomatism on the parent body we also analysed four host chondrite samples that do not give i xe ages in these samples the system appears to have been disturbed by shock it has been suggested previously that the igneous clasts are derived from an early generation of partially melted asteroids we do not have direct evidence that the clasts we examined were necessarily derived from a partially differentiated body only that they were derived from cooling of a silicate melt the clasts could thus be the products of any one of several proposed models for chondrule formation our results indicate that processes akin to chondrule formation in that they involve rapid cooling of a silicate melt were ongoing at the same time as cai formation lending support to the suggestion that al mg chondrule ages indicate either heterogeneous distribution of 26 al or resetting of the al mg system after chondrule formation

dirtmap the geological record of dust atmospheric dust is an important feedback in the climate system potentially affecting the radiative balance and chemical composition of the atmosphere and providing nutrients to terrestrial and marine ecosystems yet the potential impact of dust on the climate system both in the anthropogenically disturbed future and the naturally varying past remains to be quantified the geologic record of dust provides the opportunity to test earth system models designed to simulate dust records of dust can be obtained from ice cores marine sediments and terrestrial loess deposits although rarely unequivocal these records document a variety of processes source transport and deposition in the dust cycle stored in each archive as changes in clay mineralogy isotopes grain size and concentration of terrigenous materials although the extraction of information from each type of archive is slightly different the basic controls on these dust indicators are the same changes in the dust flux and particle size might be controlled by a combination of a source area extent b dust emission efficiency wind speed and atmospheric transport c atmospheric residence time of dust and or d relative contributions of dry settling and rainout of dust similarly changes in mineralogy reflect a source area mineralogy and weathering and b shifts in atmospheric transport the combination of these geological data with process based forward modelling schemes in global earth system models provides an excellent means of achieving a comprehensive picture of the global pattern of dust accumulation rates their controlling mechanisms and how those mechanisms may vary regionally the dust indicators and records of terrestrial and marine palaeoenvironments dirtmap data base has been established to provide a global palaeoenvironmental data set that can be used to validate earth system model simulations of the dust cycle over the past 150 000 years

significance of iron isotope mineral fractionation in pallasites and iron meteorites for the core mantle differentiation of terrestrial planets abstract seven bulk chondrites with 57 fe 54 fe values between 0 1 and 0 relative to irmm 14 tend to be slightly lighter than 11 bulk iron meteorites which have 57 fe 54 fe values ranging from 0 04 to 0 2 at the mineral scale taenite from two iron meteorites cranbourne and toluca shows 57 fe 54 fe values heavier by up to 0 3 than their kamacite counterpart thus calling into question the significance of bulk iron meteorite data on three pallasites esquel marjalahti and springwater we measured a heavier iron isotope composition for the metal fractions compared to the coexisting olivines as previously observed on two other pallasites eagle station and imilac but the range of 57 fe 54 fe differences from 0 32 to 0 07 is larger than that originally found troilite from two pallasites appears to be even heavier than the metal fraction whereas schreibersite is lighter than its olivine counterpart there is thus a general tendency for minerals within a given rock to show a heavier fe isotope composition as the coordination number of fe increases although troilite is an exception to this rule iron meteorites are classically considered as remnants of asteroid cores and pallasites as core mantle interfaces the simultaneous finding that the metal fractions of pallasites have a higher 57 fe 54 fe signature than the coexisting olivines and that the iron meteorites are slightly heavier than chondrites could be taken as an indication that planetary core mantle differentiation is accompanied by sizeable iron isotope fractionation in this hypothesis mass balance constraints imply that resultant planetary mantles should be isotopically lighter than the chondritic starting material that is not observed however since all planetary mantles analyzed so far have 57 fe 54 fe values equivalent to or heavier than those of chondrites it thus appears that the moderate temperature and pressure metal silicate fractionation that occurred in pallasite and iron parent bodies is not readily transposable to planets as far as fe isotopes are concerned instead these mantle signatures could reflect equilibrium fractionation at a higher temperature or the lack of a global core mantle equilibration at the planetary scale overall these new results show that the mass dependent isotopic scatter observed among inner solar system bodies from the bulk rock to the planetary scale 0 3 57 fe 54 fe is more restricted than previously thought this likely confirms a homogenization process that occurred in the protoplanetary accretion disk between refractory inclusion condensation and chondrule formation