mineral chemistry and the origin of enstatite in unequilibrated enstatite chondrites abstract a comprehensive study of the petrography cathodoluminescence cl rare earth element ree abundances and magnesium and silicon isotopic compositions of enstatite the major mineral in unequilibrated enstatite chondrites uecs is reported for comparison observations were also made in equilibrated enstatite chondrites eecs and aubrites in uecs there are no ree patterns or abundances that uniquely characterize the cl color and intensity grain size or occurrence of enstatite red enstatite is dominant in uecs and blue enstatite in eecs three ree patterns represent the diversity observed in uec enstatite many grains are depleted in one or more of the three most volatile rees under reducing conditions i e yb eu and sm all ree patterns are compatible with the fractional crystallization during chondrule formation of melts whose precursors either had flat ree patterns or were depleted in the most volatile rees no evidence was found to suggest that enstatite grains require nebular condensation or multiple reservoirs as suggested by others magnesium and silicon isotopic ratios are normal therefore excluding the role of evaporation in separating the rees this fractionation was most likely accomplished during condensation of the chondrule precursors our data combined with synthetic experiments support the idea that coexisting red and blue cl enstatites formed by crystallization from a single melt most of the red enstatite was converted to blue by diffusion and recrystallization to form the more equilibrated e chondrites it is not clear why enstatite is depleted in the most volatile rees while oldhamite a highly refractory mineral which is the major carrier of ree in e chondrites commonly has enrichments of these elements

a 100 kyr periodicity in the flux of extraterrestrial 3he to the sea floor most of the helium 3 in oceanic sediments comes from interplanetary dust particles idps and can therefore be used to infer the accretion rate of dust to the earth through time 3he records from slowly accumulating pelagic clays indicate that the accretion rate varies considerably over millions of years probably owing to cometary and asteroidal break up events muller and macdonald have proposed that periodic changes in this accretion rate due to a previously unrecognized 100 kyr periodicity in the earth s orbital inclination might account for the prominence of this frequency in climate records of the past million years here we report variations in the 3 he flux to the sea floor that support this idea we find that the flux recorded in rapidly accumulating quaternary sediments from the mid atlantic ridge oscillates with a period of about 100 kyr we cannot yet say however whether the 100 kyr climate cycle is a consequence of a cause of or an effect independent of these periodic changes

glacial to holocene implications of the new 27000 year dust record from the epica dome c east antarctica ice core insoluble dust concentrations and volume size distributions have been measured for the new 581 m deep dome c epica ice core antarctica over the 27000 years spanned by the record microparticle measurements from 169 levels to date confirm evidence of the drastic decrease in bulk concentration from the last glacial maximum lgm to the holocene interglacial by a factor of more than 50 in absolute value and of about 26 in flux unique new features revealed by the epica profile include a higher dust concentration during the antarctic cold reversal phase acr by a factor of 2 with respect to the holocene average this event is followed by a well marked minimum that appears to be concomitant with the methane peak that marks the end of the younger dryas in the northern hemisphere particle volume size distributions show a mode close to 2 m in diameter with a slight increase from the lgm to the holocene the lgm holocene concentration ratio appears to be dependent on particle size and for diameters from 2 to 5 m it changes from 50 to 6 glacial samples are characterised by well sorted particles and very uniform distributions while the interglacial samples display a high degree of variability and dispersion this suggests that different modes of transport prevailed during the two climatic periods with easier penetration of air masses into antarctica in the holocene than during glacial times assuming that southern south america remained the main dust source for east antarctica over the time period studied the higher dust content recorded during the acr which preceded the younger dryas period represents evidence of a change in south america environmental conditions at this time a wet period and likely mild climate in south america is suggested at circa 11 5 11 7 kyr bp corresponding to the end of the younger dryas the holocene part of the profile also shows a slight general decrease in concentration but with increasingly large particles that may reflect gradual changes at the source

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

accretion rate of cosmic spherules measured at the south pole micrometeorites are terrestrially collected extraterrestrial particles smaller than about 1 mm which account for most of the mass being accreted to the earth1 2 compared with meteorites micrometeorites more completely represent the earth crossing meteoroid complex3 4 and should include fragments of asteroids comets mars and our moon as well as pre solar and interstellar grains3 6 previous measurements of the flux of micrometeoroids that survive to the earth s surface have large uncertainties owing to the destruction of particles by weathering7 8 9 inefficiencies in magnetic collection or separation techniques7 8 9 low particle counts10 11 poor age constraint7 8 9 12 13 or highly variable concentrating processes12 13 here we describe an attempt to circumvent these problems through the collection of thousands of well preserved and dated micrometeorites from the bottom of the south pole water well which supplies drinking water for the scott amundsen station using this collection we have determined precise estimates of the flux and mass distribution for 50 700 m cosmic spherules melted micrometeorites allowing for the expected abundance of unmelted micrometeorites14 in the samples our results indicate that about 90 of the incoming mass of submillimetre particles evaporates during atmospheric entry our data indicate the loss of glass rich and small stony spherules from deep sea deposits7 8 and they provide constraints for models describing the survival probability of micrometeoroids15 16

rare earth element geochemistry and petrogenesis of miles iie silicate inclusions an ion probe study of rare earth element ree geochemistry of silicate inclusions in the miles he iron meteorite was carried out individual mineral phases among inclusions have distinct ree patterns and abundances most silicate grains have homogeneous ree abundances but show considerable intergrain variations between inclusions a few pyroxene grains display normal igneous ree zoning phosphates whitlockite and apatite are highly enriched in rees 50 to 2000 x ci with a relatively light rare earth element lree enriched ree pattern they usually occurred near the interfaces between inclusions and fe host in miles albitic glasses exhibit two distinctive ree patterns a highly fractionated lree enriched ci normalized la sm similar to 15 pattern with a large positive eu anomaly and a relatively heavy rare earth element hree enriched pattern ci normalized lu gd similar to4 with a positive eu anomaly and a negative yb anomaly the glass is generally depleted in rees relative to ci chondrites

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

francoisite ce a new mineral species from la creusaz uranium deposit valais switzerland and from radium ridge flinders ranges south australia description and genesis the new mineral francoisite ce ce nd ca uo 2 3 o oh po 4 2 6h 2 o is the ce analog of francoisite nd it has been discovered simultaneously at the la creusaz uranium deposit near les marecottes in valais switzerland and at the number 2 uranium workings radium ridge near mt painter arkaroola area northern flinders ranges in south australia francoisite ce is a uranyl bearing supergene mineral that results from the alteration under oxidative conditions of ree and u 4 bearing hypogene minerals allanite ce monazite ce uraninite at les marecottes monazite ce ishikawaite samarskite and an unknown primary u mineral at radium ridge the ree composition of francoisite ce results from a short aqueous transport of ree leached out of primary minerals most likely monazite ce at radium ridge and allanite ce at la creusaz with fractionation among ree resulting mainly from aqueous transport with only limited ce loss due to oxidation to ce 4 during transport

extraterrestrial 3he in seafloor sediments evidence for correlated 100 kyr periodicity in the accretion rate of interplanetary dust orbital parameters and quaternary climate we have determined the helium abundance and isotopic composition of seafloor carbonate sediments from the flanks of the ontong java plateau western equatorial pacific ocean odp site 806 these results provide a two million year record of the burial flux of extraterrestrial 3he which we believe is a proxy for the terrestrial accretion rate of interplanetary dust particles the 3he burial flux prior to 700 ka was relatively low 0 5 pcc cm 2 kyr 1 but from 700 ka to the present the burial flux gradually increased to a value of 1 0 pcc cm 2 kyr 1 100 kyr periodicity in the 3he burial flux is apparent over the last 700 kyr and correlates with the oxygen isotope record of global climate with high 3he burial fluxes associated with interglacial periods this periodicity and phase are consistent with previous 3he measurements in north atlantic sediments although 100 kyr periodicity in 3he burial flux is in agreement with recent predictions of the accretion rate of interplanetary dust based on a model of the orbital evolution of asteroidal debris the measurements and predictions differ by one half cycle in phase nevertheless our observations suggest the terrestrial accretion rate of interplanetary dust is controlled by orbital eccentricity and or inclination relative to the solar system invariable plane such control is a necessary but not sufficient condition for the hypothesis of muller and macdonald 1995 that variations in extraterrestrial dust accretion modulates terrestrial climate with a 100 kyr period we also identify several brief 25 kyr intervals of strongly enhanced 3he burial possibly related to random and transient fluctuations in the accretion rate of asteroidal or cometary dust particles

hf w sm nd and rb sr isotopic evidence of late impact fractionation and mixing of silicates on iron meteorite parent bodies abstract we report the first sm nd and rb sr isotopic analyses of silicate inclusions in four iie iron meteorites miles weekeroo station a and b and watson we also report the hf w isotopic composition of a silicate inclusion from watson and 182 w 184 w of the host feni metal in all four iies the host metal in watson has a negative w value 2 21 0 24 similar to or higher than other iron meteorites 1 35 and consistent with segregation of metal from silicate early in solar system history however the large silicate inclusion in the watson iie iron yielded a chondritic w value 0 50 0 55 thus indicating a lack of equilibration with the feni host within the practical lifetime of activity of the parent 182 hf 50 ma one of the silicate inclusions in miles is roughly chondritic in major element composition has a present day nd of 10 3 relatively non radiogenic 87 sr 86 sr 0 714177 13 and a t chur age of 4270 ma two silicate inclusions from weekeroo station and one from watson exhibit fractionated sm nd and rb sr ratios and more radiogenic 87 sr 86 sr 0 731639 12 to 0 791852 11 and non radiogenic nd values 5 9 to 13 4 the silicate inclusion in watson has a t chur age of 3040 ma in agreement with previously determined 4 he and 40 ar gas retention ages indicative of a late thermal event a later event is implied for the two silicate inclusions in weekeroo station which yield indistinguishable t chur ages of 698 and 705 ma silicate inclusions in iie iron meteorites formed over a period of 3 billion yr by impacts involving an h chondrite parent body and an feni metal parent body the lile enriched nature of some of these silicates suggests several stages of melting mixing and processing however there is little evidence to suggest that the silicates in the iie irons were ever in equilibrium with the host feni metal

discriminating between different genetic types of marine ferro manganese crusts and nodules based on rare earth elements and yttrium marine ferro manganese fe mn crusts and nodules are metal rich chemical sediments that are archives of paleoceanographic proxies and potential metal resources and targets of deep sea mining traditionally crusts and nodules are subdivided into hydrogenetic diagenetic and hydrothermal types because these are characterized by different compositions and hence economic resource potential a useable genetic classification is not only a tool for geochemical studies but may also help to characterize potential exploration targets we propose two easy to use yet robust discrimination diagrams based on geochemical relationships controlling the rare earths and yttrium rey inventory of marine fe mn oxyhydr oxide deposits the rey are a set of trace elements that show coherent behavior are routinely determined in geochemical studies and for which the analytical quality can easily be evaluated graphs of ce anomaly vs nd concentration and ce anomaly vs y anomaly effectively discriminate between the different types of precipitates regardless of their diverse mineralogical composition both hydrogenetic crusts and nodules show positive ce anomalies negative y anomalies and high nd concentrations of 100 mg kg 1 although nodules tend to have slightly lower nd concentrations than crusts in marked contrast hydrothermal deposits generally yield negative ce anomalies positive y anomalies and low nd concentrations of 10 mg kg 1 in spite of their large geochemical mineralogical and sedimentological diversity diagenetic nodules show negative ce anomalies negative y anomalies and intermediate nd concentrations between 10 and 100 mg kg 1 we discuss the geochemical background of these diagrams the respective sources of rey in the different precipitates and address the processes that control their rey inventory besides the three end members we also use rey systematics to define mixed type diagenetic hydrogenetic nodules and classify well studied international reference standards

chronology and petrology of silicates from iie iron meteorites evidence of a complex parent body evolution iie iron meteorites contain silicate inclusions the characteristics of which suggest a parent body similar to that of h chondrites however these silicates show a wide range of alteration ranging from netschaevo and techado the inclusions of which are little altered to highly differentiated silicates like those in kodaikanal weekeroo station and colomera which have lost metal and sulfur and are enriched in feldspar we find these inclusions to show varying degrees of shock alteration we made 39ar 40ar age determinations of watson techado miles colomera and sombrerete watson has an ar ar age of 3 677 0 007 gyr similar to previously reported ages for kodaikanal and netschaevo we suggest that the various determined radiometric ages of these three meteorites were probably reset by a common impact event the space exposure ages for these three meteorites are also similar to each other and are considerably younger than exposure ages of other iies 39ar 40ar ages inferred for the other four meteorites analyzed are considerably older than watson and are techado 4 49 0 01 gyr miles 4 405 0 012 gyr colomera 4 470 0 010 gyr and sombrerete 4 541 0 0012 gyr these ages are in fair agreement with previously reported rb sr isochron ages for colomera and weekeroo station although several mechanisms to form iie meteorites have been suggested it is not obvious that a single mechanism could produce a suite of meteorites with very different degrees of silicate differentiation and with isotopic ages that differ by 0 8 gyr we suggest that those iies with older isotopic ages are a product of partial melting and differentiation within the parent body followed by mixing of silicate and metal while both were relatively hot netschaevo and watson may have formed by this same process or by impact mixing 4 5 gyr ago but their isotopic ages may have been subsequently reset by shock heating kodaikanal apparently is required to have formed more recently in which case impact melting and differentiation seems the only viable process we see no compelling reasons to believe that iie silicate and metal derived from different parent bodies or that the parent body of iies was the same as that of h chondrites

meteoric smoke fallout over the holocene epoch revealed by iridium and platinum in greenland ice an iridium anomaly at the cretaceous tertiary boundary layer has been attributed to an extraterrestrial body that struck the earth some 65 million years ago1 it has been suggested that during this event the carrier of iridium was probably a micrometre sized silicate enclosed aggregate2 or the nanophase material of the vaporized impactor3 but the fate of platinum group elements such as iridium that regularly enter the atmosphere via ablating meteoroids remains largely unknown here we report a record of iridium and platinum fluxes on a climatic cycle timescale back to 128 000 years ago from a greenland ice core4 we find that unexpectedly constant fallout of extraterrestrial matter to greenland occurred during the holocene whereas a greatly enhanced input of terrestrial iridium and platinum masked the cosmic flux in the dust laden atmosphere of the last glacial age we suggest that nanometre sized meteoric smoke particles5 6 formed from the recondensation of ablated meteoroids in the atmosphere at altitudes 70 kilometres are transported into the winter polar vortices by the mesospheric meridional circulation7 and are preferentially deposited in the polar ice caps this implies an average global fallout of 14 5 kilotons per year of meteoric smoke during the holocene

mineralogy of silicate inclusions of the colomera iie iron and crystallization of cr diopside and alkali feldspar from a partial melt we studied the mineralogy mineral chemistry and compositions of 48 interior silicate inclusions and a large k rich surface inclusion from the colomera he iron meteorite common minerals in the interior silicate inclusions are cr diopside and na plagioclase albite they are often enclosed by or coexist with albitic glasses with excess silica and minor fe mg components this mineral assemblage is similar to the andesitic material found in the caddo county iab iron meteorite for which a partial melt origin has been proposed the fairly uniform compositions of cr diopside ca44mg46fe10 and na plagioclase or 2 5 ab 90 0 an 7 5 to or 3 5 ab 96 1 an 0 4 in colomera interior inclusions and the angular boundaries between minerals and metal suggest that diopside and plagioclase partially crystallized under near equilibrium conditions from a common melt before emplacement into molten metal the melt crystal assemblage has been called crystal mush the bulk compositions of the individual composite inclusions form an array between the most diopside rich inclusion and plagioclase this is consistent only with a simple mechanical mixing relationship not a magmatic evolution series we propose a model in which partly molten metal and crystal mush were mixed together by impact on the he parent body other models involving impact melting of the chondritic source material followed by growth of diopside and plagioclase do not easily explain near equilibrium growth of diopside and na plagioclase followed by rapid cooling in the k rich surface inclusion k feldspar orthopyroxene and olivine were found together with diopside for the first time k feldspar sanidine or 92 7 ab 7 2 an 0 1 to or 87 3 ab 11 0 an 1 7 occurs in an irregular veinlike region in contact with large orthopyroxene crystals of nearly uniform composition ca1 3mg80 5fe17 8 to ca3 1mg78 1fe18 9 and intruding into a relict olivine with deformed oval shape silica and subrounded cr diopside are present within such k feldspar regions some enrichments of the albite component have been detected at the end of curved elongated nodules of k feldspar intruded into the mafic silicates the textural relationships suggest that a k rich melt was present a k rich melt is neither the first melt of a chondritic system nor a differentiation product of a na rich partial melt of chondritic material the k rich material may have originated as a fluid phase that leached k from surrounding materials and segregated by a mechanism similar to that proposed for the na rich inclusions copyright c 2003 elsevier science ltd

iridium enrichment in volcanic dust from blue ice fields antarctica and possible relevance to the k t boundary event abstract blue ice fields in antarctica well known as stranding zones of antarctic meteorites contain ice that is several tens to hundreds of thousand years old which records numerous events that have taken place since its formation among the most important structures on the ice fields are dust bands which are mostly of volcanic origin and consist of small volcanic glass shards and lithic fragments petrographic and chemical studies of a number of dust bands during earlier investigations have shown that significant ash layers are deposited at distances of up to several thousand kilometers from the source volcanoes samples of dust layers taken in the lewis cliff beardmore glacier area in antarctica analyzed in the course of this work for major and trace elements were identified as consisting of volcanic ash probably originating from the pleiades melbourne volcanic province northern victoria land some of these dust samples were found to contain iridium in concentrations of up to 7 5 ppb a positive correlation between ir and se as well as enrichments in as sb and other volcanogenic elements has been observed the dust samples investigated here have very small grain size consistent with the distance from the source volcanoes the small grain size of the dust suggests that the ir enrichment is a surface effect and was probably caused by condensation from a vapor phase this is the first time that significant ir enrichments have been found in volcanic dust which demonstrates that ir and possibly also other platinum group metals may be present in some volcanic ash deposits although this has been doubted by the proponents of the pure impact theory for the k t boundary event the results of this study suggest that the ir in the k t boundary clays is not necessarily of cosmic origin but alternatively may have originated from mantle reservoirs that were tapped during extensive volcanic eruptions which may been triggered by impact events

petrogenesis of silicate inclusions in the weekeroo station iie iron meteorite differentiation remelting and dynamic mixing the weekeroo station iie iron meteorite contains a variety of felsic and mafic inclusions enclosed in an feni metal host petrographic emp and sims data suggest that the petrogenesis of the silicates was complex and included differentiation remelting feo reduction and dynamic mixing of phases differentiation produced a variety of olivine free inclusion assemblages ranging from pyroxene 1 plagioclase 1 tridymite with peritectic compositions to coarse orthopyroxene to plagioclase 1 tridymite and its glassy equivalent individual phases have similar trace element abundances and patterns despite large variations in inclusion textures modes and bulk compositions probably as a result of mechanical separation of pre existing phases in an impact event that dynamically mixed silicates with the metallic host trace element data imply that augite and plagioclase grains in different inclusions crystallized from the same precursor melt characterized by relatively unfractionated ree abundances of 20 30 3 ci chondrites except for a negative eu anomaly such a precursor melt could have been produced by 2 5 equilibrium partial melting of an h chondrite silicate protolith or by higher degrees of partial melting involving subsequent fractional crystallization glass appears to have formed by the remelting of pre existing plagio clase and orthopyroxene in a process that involved either disequilibrium or substantial melting of these phases during remelting silicate melt reacted with the feni metal host and feo was reduced to fe metal following remelting and metal silicate mixing inclusions apparently cooled at different rates in a near surface setting on the parent body glass or pigeonite bearing inclusions cooled more rapidly 2 5 c hr between 1000 850 c than pigeonite free largely crystalline inclusions the results of this study point to two likely models for forming iie iron meteorites both involving collision between an feni metal impactor and either a differentiated or undifferentiated silicate rich target of h chondrite affinity each model has difficulties and it is possible that both are required to explain the diverse iie group copyright 1999 elsevier science ltd

arsenian monazite ce and xenotime y ree arsenates and carbonates from the tisovec rejkovo rhyolite western carpathians slovakia composition and substitutions in the ree y xo4 system x p as si nb s abstract a unique ree y th p as si nb s accessory assemblage was identified in a small body of lower triassic a type rhyolite of the silicic superunit near tisovec rejkovo central slovakia arsenian monazite ce phosphatian gasparite ce and arsenian xenotime y phosphatian chernovite y solid solutions in association with ree carbonates bastnasite parisite rontgenite synchysite and rare cerianite ce form anhedral to subhedral grains and aggregates 0 3 mm scattered in the groundass or as intergrowths with zircon and fe ti oxides compositions show a wide asp 1 substitution in monazite gasparite and xenotime chernovite solid solutions atom as as p 0 00 to 0 73 and 0 10 to 0 94 respectively the presence of s in monazite gasparite s s 0 14 apfu together with ca enrichment indicates clinoanhydrite substitution cas ree y 1 p as 1 rather than the incorporation of brabantite along the cath ree y 2 exchange vector moreover the th and nb rich members reveal thorite and fergusonite substitutions thsi y ree 1 p as 1 and nb p as 1 respectively the as rich ree phases originated probably during the post magmatic alteration of primary monazite ce and xenotime y by as rich high fo2 fluids whereas cerianite ce and the ree carbonates are products of a later hydrothermal overprint of the rhyolite by co2 rich solutions

corundum bearing residues produced through the evaporation of natural and synthetic hibonite we have produced corundum bearing residues through the evaporation of natural and synthetic hibonite samples the sequence of major element losses as well as volatility related trace element fractionations in these residues are similar to those previously observed in residues from the evaporation of chondritic starting material which suggests that the processes by which these fractionations occur may be largely independent of the starting material used however the mineralogy of the residues does depend on the composition of the starting material and to some extent on the conditions under which evaporation took place similarly the degree of isotopic mass fractionation observed in the residues is composition dependent this observation means that it may be possible to use isotopic data for several elements to constrain the compositions of precursor materials of ca al rich inclusions which have an evaporation origin although corundum bearing inclusions are known their origins are complex and variable and the scarcity of such inclusions indicates that melting of hibonite with or without concomitant evaporation must have been a rare process in the solar nebula by evaporating mixtures of synthetic oxides of the rare earth elements we have reproduced the patterns of group iii inclusions and some of the characteristics of ultrarefractory patterns however the extreme conditions required to do so indicate that refractory inclusions with these patterns probably have a condensation rather than evaporation origin

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

lanthanide and actinide chemistry at high c o ratios in the solar nebula abstract chemical equilibrium calculations were performed to study the condensation chemistry of the ree and actinides under the highly reducing conditions which are necessary for the formation of the enstatite chondrites 1 2 our calculations confirm that the ree and actinides condensed into oldhamite cas the major ree and actinide host phase in enstatite chondrites at a carbon oxygen co ratio 1 in an otherwise solar gas five basic types of ree abundance patterns several of which are analogous to ree abundance patterns observed in the ca al rich inclusions cais in carbonaceous chondrites are predicted to occur in meteoritic oldhamites all of the reported ree patterns in oldhamites in enstatite chondrites can be interpreted in terms of our condensation calculations the observed patterns fall into 3 of the 5 predicted categories the reported th and u enrichments and ratios in meteoritic oldhamites are also consistent with predictions of the condensation calculations finally pure ree sulfides are predicted to condense in the 10 6 to 10 9 bar range and may be found in enstatite chondrites if they formed in this pressure range

petrology of silicate inclusions in the sombrerete ungrouped iron meteorite implications for the origins of iie type silicate bearing irons the petrography and mineral and bulk chemistries of silicate inclusions in sombrerete an ungrouped iron that is one of the most phosphate rich meteorites known was studied using optical scanning electron microscopy sem electron microprobe analysis empa and secondary ion mass spectrometry sims techniques inclusions contain variable proportions of alkalic siliceous glass 69 vol of inclusions on average aluminous orthopyroxene 9 wo1 4fs2535 up to 3 wt al plagioclase 8 mainly an7092 cl apatite 7 chromite 4 yagiite 1 phosphaterich segregations 1 ilmenite and merrillite ytterbium and sm anomalies are sometimes present in various phases positive anomalies for phosphates negative for glass and orthopyroxene which possibly reflect phosphate melt gas partitioning under transient reducing conditions at high temperatures phosphate rich segregations and different alkalic glasses k rich and na rich formed by two types of liquid immiscibility yagiite a k mg silicate previously found in the colomera iie iron appears to have formed as a late stage crystallization product possibly aided by na k liquid unmixing trace element phase compositions reflect fractional crystallization of a single liquid composition that originated by low degree 48 equilibrium partial melting of a chondritic precursor compositional differences between inclusions appear to have originated as a result of a filter press differentiation process in which liquidus crystals of cl apatite and orthopyroxene were less able than silicate melt to flow through the metallic host between inclusions this process enabled a phosphoran basaltic andesite precursor liquid to differentiate within the metallic host yielding a dacite composition for some inclusions solidification was relatively rapid but not so fast as to prevent flow and immiscibility phenomena sombrerete originated near a cooling surface in the parent body during rapid probably impact induced mixing of metallic and silicate liquids we suggest that sombrerete formed when a planetesimal undergoing endogenic differentiation was collisionally disrupted possibly in a breakup and reassembly event simultaneous endogenic heating and impact processes may have widely affected silicate bearing irons and other solar system matter

gasparite la la aso4 a new mineral from mn ores of the ushkatyn iii deposit central kazakhstan and metamorphic rocks of the wanni glacier switzerland

plutonium 238 observations as a test of modeled transport and surface deposition of meteoric smoke particles 1 there are large uncertainties in the transport and surface deposition of upper atmospheric particles used to construct climate proxies here we use a 3 d chemistry climate model ccm to simulate the transport and deposition of plutonium 238 oxide nanoparticles formed after the ablation of a power unit in the upper stratosphere 11 s in 1964 the model reproduces both the observed hemispheric asymmetry and time scale of pu 238 deposition we then use the ccm to investigate the transport of meteoric smoke particles msps from the upper mesosphere the strongest msp deposition is predicted to occur at middle latitudes providing a significant source of fe fertilization to the southern ocean the model also predicts substantially more deposition in greenland than in antarctica by a factor of 15 in agreement with ice core measurements showing that climate proxy measurements from a limited number of sites must be interpreted with care

accretion of interplanetary dust in polar ice measurements of helium isotopes in particles separated from polar ice demonstrate that extraterrestrial he dominates the he flux at the gisp2 greenland and vostok antarctica ice core sites replicate measurements of late holocene ice samples yield he fluxes of 0 62 0 27 10 12 cm stp cm 2 ka 1 gisp2 and 0 77 0 25 10 12 cm stp cm 2 ka 1 vostok similar to results from marine sediments these are the first detailed measurements of he in particles from ice core samples and they demonstrate the utility of the ice core record for evaluating the temporal history of the extraterrestrial dust flux results from vostok samples from 1096 1403 m depth 75 97 ka b p are similar to the late holocene data with the exception of two highly anomalous results from 1307 m the latter probably indicate the presence of rare large or gas rich extraterrestrial particles

rhenium 187 osmium 187 in iron meteorites and the strange origin of the kodaikanal meteorite a set of iron meteorites was investigated for re os isotopes and provides a well defined isochron age of 4 624 0 017 ba and an initial 187os 188os ratio of 0 095636 0 00009 actual ages may be a few percent lower due to uncertainty on the 187re decay constant within the small sample number presented here there is no evidence for age differences between classes a more detailed study of the meteorite kodaikanal shows that the metal reservoir of this meteorite formed approximately at the same time as the other iron meteorites in contrast with the silicate inclusions which display a formation age of 3 67 ba with all other chronometers a collisional origin is in agreement with the data on this meteorite major secondary events do not affect the re os system at the bulk rock scale in metal as it is the sole significant reservoir of these two elements a re os and rb sr investigation of meteoritic troilite exhibits disturbed chronometric systems which we attribute to the terrestrial history of the meteorite

30 000 years of cosmic dust in antarctic ice polar ice provides an archive for the influx of cosmic dust here we present a high resolution glacial to interglacial record of cosmic dust using helium isotope analysis of the european project for ice coring in antarctica epica ice core drilled in dronning maud land we obtained a relatively constant 3he flux over the past 30 000 years this finding excludes 3he as a pacemaker of late pleistocene glacial cycles rather it supports 3he as a constant flux parameter in paleoclimatic studies a last glacial to holocene shift of the 4he non sea salt ca2 ratio appears to indicate a glacial to interglacial change in the terrestrial dust source

dust size evidence for opposite regional atmospheric circulation changes over east antarctica during the last climatic transition three east antarctic ice cores dome b epica dome c and komsomolskaia give evidence for a uniform dust input to the polar plateau during the last glacial maximum lgm holocene transition 20 to 10 kyr bp and the 87sr 86sr versus 143nd 144nd isotopic signature of the mineral particles highlights a common provenance from southern south america at that time however the size distribution of dust from the three ice cores highlights important differences within the east antarctic during the lgm and shows clearly opposite regional trends during the climatic transition between dome b and dome c the timing of these changes is also different a geographical diversity also arises from the different phasing of the short term multi secular scale dust size oscillations that are superposed at all sites on the main trends of glacial to interglacial changes we hypothesize the dust grading is controlled by size fractionation inresponse to its atmospheric pathway either in terms of horizontal trajectory or in altitude of transport such mechanism is supported also by the dust size changes observed during a volcanic event recorded in vostok ice ice core dust size data suggest preferential upper air subsidence over the edc kms region and easier penetration of relatively lower air masses to the db area during the lgm at the end of the last glacial period and during the climatic transition the region of relatively higher subsidence progressively moved southward the scenario proposed supported also by the lgm holocene regional changes of snow accumulation likely operates even at sub millennial time scale

the osmium isotopic composition of the continental crust osmium isotopic compositions and concentrations have been determined for deltaic and continental shelf sediments from three major rivers the amazon changjiang and mississippi and for two loesses from the upper mississippi river valley the loesses have heavy mineral and clay compositions characteristic of mississippi river and delta sediment concentrations range from 15 to 120 pg os g and 187os 186os ratios range from 8 2 to 10 9 sediments which are polluted surface sediment from the changjiang estuary or which have scavenged metals from seawater gulf of mexico slope surface sediment and distal amazon shelf sediment have high osmium concentrations and less radiogenic isotopic compositions purely terrigenous sediments have 15 90 pg os g and 187os 186os 10 0 10 9 north american loess and mississippi delta sediment osmium isotopic compositions are indistinguishable we believe that 187os 186os 10 11 is a good average for currently eroding upper continental crust these sediments have neodymium isotopic compositions close to the global mean for river sediment terrigenous 187os 186os is significantly more radiogenic than seawater 187os 186os 8 6 requiring a nonriverine source of osmium to seawater terrigenous osmium is also significantly more radiogenic than bulk pelagic clay osmium we use the improved estimate of terrigenous 187os 186os to recalculate the flux of extraterrestrial osmium to pacific marine sediment if the residence age of osmium in an upper crustal region is similar to the neodymium model age of a sediment derived from that region a model dependent upper crustal 187re 186os ratio can be calculated for the model ages of the sediments analyzed in this study tdm 1 5 1 7 ga model 187re 186os ratios are 340 360 and can be used to correct for bias resulting from the preferential erosion of young crust the 187os 186os ratio of 2 2 ga crust with 187re 186os 400 is 14 2 we have also used the data from this study to estimate upper crustal osmium and rhenium concentrations of 50 pg g and 390 pg g respectively

meteoric smoke deposition in the polar regions a comparison of measurements with global atmospheric models the accumulation rate of meteoric smoke particles msps in ice cores determined from the trace elements ir and pt and superparamagnetic fe particles is significantly higher than expected from the measured vertical fluxes of na and fe atoms in the upper mesosphere and the surface deposition of cosmic spherules the whole atmosphere community climate model waccm with the community aerosol and radiation model for atmospheres carma has been used to simulate msp production transport and deposition using a global msp input of 7 9 t d 1 based on these other measurements the modeled msp deposition rates are smaller than the measurements by factors of 32 in greenland and 12 in antarctica even after reanalysis of the ir pt ice core data with inclusion of a volcanic source variations of the model deposition scheme and use of the united kingdom chemistry and aerosols ukca model do not improve the agreement direct removal of msp nucleated polar stratospheric cloud particles to the surface gives much better agreement but would result in an unfeasibly high rate of nitrate deposition the unablated fraction of cosmic dust 35 t d 1 would provide sufficient ir and pt to account for the antarctic measurements but the relatively small flux of these large 3 m particles would lead to greater variability in the ice core measurements than is observed although this would be partly offset if significant fragmentation of cosmic dust particles occurred during atmospheric entry future directions to resolve these discrepancies between models and measurements are also discussed

crystal chemistry of the monazite and xenotime structures monazite and xenotime the re p04 dimorphs are the most ubiquitous rare earth re minerals yet accurate structure studies of the natural phases have not been reported here we report the results of high precision structure studies of both the natural phases and the synthetic re p04 phases for all individual stable rare earth elements monazite is monoclinic p2 n and xenotime is isostructural with zircon space group 14 amd both atomic arrangements are based on 001 chains of intervening phosphate tetrahedra and re polyhedra with a reogpolyhedron in xenotime that accommodates the heavy lanthanides tb lu in the synthetic phases and a re09 polyhedron in monazite that preferentially incorporates the larger light rare earth elements la gd as the structure transforms from xenotime to monazite the crystallographic properties are comparable along the 00i chains with structural adjustments to the different sizes of re atoms occurring principally in 00i there are distinct similarities between the structures that are evident when their atomic arrangements are projected down 001 in that projection the chains exist in 100 planes with two planes per unit cell in monazite the planes are offset by 2 2 a along 010 relative to those in xenotime in order to accommodate the larger light re atoms the shift of the planes in monazite allows the re atom in that phase to bond to an additional 02 atom to complete the re09 polyhedron

comparative petrology of silicates in the udei station iab and miles iie iron meteorites implications for the origin of silicate bearing irons abstract the textures and mineral chemistries of silicate inclusions in the udei station iab and miles fractionated iie iron meteorites were studied using optical and electron microscopy sem empa and la icp ms techniques to better understand the origin of silicate bearing irons inclusions in udei station include near chondritic basaltic gabbroic feldspathic orthopyroxenitic and harzburgitic lithologies in miles most inclusions can be described as feldspathic pyroxenite or pyroxene enriched basalt gabbro the trace element compositions of both orthopyroxene and plagioclase grains are similar in different lithologies from udei station whereas in different inclusions from miles the compositions of orthopyroxene grains are similar while those of clinopyroxene plagioclase and especially cl apatite are variable orthopyroxene in miles tends to be enriched in ree compared to that in udei station but the reverse is true for plagioclase and clinopyroxene the data can be explained by models involving partial melting of chondritic protoliths silicate melt migration and redox reactions between silicate and metal components to form phosphate the extent of heating melt migration and phosphate formation were all greater in miles silicates in miles were formed from liquids produced by 30 partial melting of a chondritic precursor brought to a peak temperature of 1250 c this silicate melt crystallized in two stages during stage 1 crystallizing minerals orthopyroxene clinopyroxene chromite and olivine were largely in equilibrium with an intercumulus melt that was evolving by igneous fractionation during slow cooling with a residence time of 20 ka at 1150 c during stage 2 following probable re melting of feldspathic materials and after the silicate mush was mixed with molten metal plagioclase and phosphate fractionally crystallized together during more rapid cooling down to the solidus in udei station despite a lower peak temperature we suggest that a model involving major collisional disruption and mixing of partly molten endogenically heated planetesimals can best explain the data for iab and fractionated iie silicate bearing irons the extent of endogenic heating was different less for the iabs and the amount of parent body disruption was different scrambling with collisional unroofing for the iab iiicd winonaite body more complete destruction for the fractionated iie body but both bodies were partly molten and incompletely differentiated at the time of impact we suggest that the post impact secondary body for iab iiicd winonaite meteorites was mineralogically zoned with ni poor metal in the center and that the secondary body for fractionated iie meteorites was a relatively small melt rich body that had separated from olivine during collisional break up

placers of cosmic dust in the blue ice lakes of greenland a concentration process occurring in the melt zone of the greenland ice cap has produced the richest known deposit of cosmic dust on the surface of the earth extraterrestrial particles collected from this region are well preserved and are collectable in large quantities the collected particles are generally identical to cosmic spheres found on the ocean floor but a pure glass type was discovered that has not been seen in deep sea samples iron rich spheres are conspicuously rare in the collected material

a nonmagmatic origin of group iie iron meteorites abstract new neutron activation data on 10 elements in 12 iie and iie related irons lead to a reclassification of several irons seymchan and lonaconing are removed from iie and leshan added four iie members are designated iie an to call attention to some anomalous properties the eight normal iie members define element ni trends generally similar to those in the nonmagmatic group iab the small negative slopes on w ni and ir ni diagrams are strongly indicative of a nonmagmatic origin of the iie irons we propose that iie irons like iab irons originated as individual pools of impact produced melt in the near surface region of a chondritic parent body the positive as ni and au ni trends are the only evidence suggesting fractional crystallization but their slopes are lower than those in magmatic group iiiab and only slightly higher than those of cu and sb in iab we suggest that the s and c contents of the iie precursor materials were much lower than those of the iab precursors thus higher temperatures were required to generate enough metallic melt to segregate into pools these higher temperatures are also reflected in the nonchondritic compositions of the silicate inclusions

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

accretion rate of extraterrestrial matter iridium deposited 33 to 67 million years ago iridium measured in 149 samples of a continuous 9 meter section of pacific abyssal clay covering the time span 33 to 67 million years ago shows a well defined peak only at the cretaceous tertiary boundary in the rest of the section iridium ranges from a minimum concentration near 0 35 nanograms per gram in the paleocene to a maximum near 1 7 in the eocene between 63 and 33 million years ago the mean iridium accumulation rate is approximately 13 nanograms per square centimeter per million years correction for terrestrial iridium leads to an extraterrestrial flux of9 3 nanograms of iridium per square centimeter per million years and an estimated annual global influx of 78 billion grams of chondritic matter consistent with recent estimates of the influx of dust meteorites and crater producing bodies with masses ranging from 10 13 to 1018 grams combining the recent flux of objects ranging in mass from 106 to 107 grams with the flux of 1014 to 1015 gram objects indicates that the number of objects is equal to 0 54 divided by the radius in kilometers to the 2 1 power periodic comet showers should increase the cometary iridium flux by a factor of 200 to 600 on a time scale of 1 to 3 million years the predicted iridium maxima more than 30 times background are not present in the intervals associated with the cretaceous tertiary boundary or the tektiteproducing late eocene events

experimental simulation of atmospheric entry of micrometeorites depending on their velocity entry angle and mass micrometeorites suffer different degrees of heating during their deceleration in the earth s atmosphere leading in most cases to significant textural mineralogical and chemical modifications one of these modifications is the formation of a magnetite shell around most micrometeorites which until now could not be reproduced neither theoretically nor experimentally the present study was designed to better understand the entry heating effects on micrometeorites and especially the formation of the magnetite shell fragments of the murchison and orgueil meteorites were used as analogue material in flash heating experiments performed in a high temperature furnace effects of temperature heating duration and oxygen fugacity were investigated these experiments were able to reproduce most of the micrometeorites textures from the vesicular fine grained micrometeorites to the totally melted cosmic spherules for the first time the formation of a magnetite shell could be observed on micrometeorite analogues we suggest that the most plausible mechanism for the formation of this shell is a peripheral partial melting with subsequent magnetite crystallization at the surface of the micrometeorite furthermore with this study it is possible to estimate the atmospheric entry conditions of micrometeorites such as the peak temperature and the duration of flash heating

thallium geochemistry in the metamorphic lengenbach sulfide deposit switzerland thallium isotope fractionation in a sulfide melt the lengenbach switzerland pb as tl zn deposit was formed from a sulfide melt at about 500 c during alpine metamorphism but details on its formation and especially the source of the metals are still under debate in this study we present two sample sets to address these questions 1 mc icp ms analyses of thallium isotopes in sulfides sulfosalts and melt inclusions from the alpine metamorphic lengenbach deposit in the binn valley of switzerland the non metamorphic wiesloch mississippi valley type deposit in southern germany and the cu and as rich mineralization at pizzo cervandone about 2 km sw of the lengenbach deposit which has been discussed as potential source of the lengenbach metals 2 la icp ms analyses of micas from the lengenbach deposit and surrounding country rocks between the deposit and the pizzo cervandone to trace potential metal bearing fluid pathways we found that tl isotope compositions expressed as 205tl values in all investigated samples range from 4 1 0 5 to 1 9 0 5 the whole variation can be seen in the lengenbach deposit alone which hence records considerable fractionation even during high temperature processes involving a sulfide melt this large range of 205tl is thought to be caused by nuclear volume dependent fractionation interestingly the common fahlores at lengenbach behave differently from all other investigated sulfosalts based on their heavy isotopic composition together with a low as s ratio they do not seem to be crystallized from the sulfide melt but are interpreted to have formed from hydrothermal fluids enriched in the heavy tl isotopes although as mobilization in the gneisses and dolomites surrounding the lengenbach deposit is evident based on secondary arsenites no traces of such a country rock fluid could be found in fissure micas at lengenbach hence considerations involving k rb rb tl as s and pb tl ratios in the sulfides and micas imply that the element enrichment in the lengenbach deposit is either pre alpine or related to peak metamorphism but occurred definitely before mica growth at lengenbach

mineral chemistry and the petrogenesis of eucrites ii cumulate eucrites abstract we carried out an ion microprobe study of rees and other selected trace and minor element concentrations in orthopyroxene augite lamellae and plagioclase of two cumulate eucrites moama and moore county in order to reevaluate the relationships between cumulate and noncumulate eucrites and among cumulate eucrites pyroxene and plagioclase in these two meteorites are more homogeneous in major minor and trace elements than in noncumulate eucrites and trace and minor element concentrations in moore county are higher than in moama although subsolidus equilibration erased and original igneous zoning it did not affect the ree patterns of these minerals both pigeonite and plagioclase of moama and moore county have higher lree hree ratios than those phases in noncumulate eucrites this indicates that cumulate eucrites derived from melts with fractionated ree patterns and thus are not related to noncumulate eucrites in addition the inconsistency between degrees of fractional crystallization deduced from major and trace elements and the differences of lree hree ratios recorded in pigeonite and plagioclase also suggest that moama and moore county did not form in the same fractional crystallization sequence this study confirms earlier observations and conclusions of ma and schmitt 1979 and poses problems for prevalent models

trace element studies of silicate rich inclusions in the guin ungr and kodaikanal iie iron meteorites a devitrified glass inclusion from the guin ungr iron consists of cryptocrystalline feldspars pyroxenes and silica and is rich in sio2 al2o3 and na2o it contains a rutile grain and is in contact with a large cl apatite the latter is very rich in rare earth elements rees 80 x ci which display a flat abundance pattern except for eu and yb which are underabundant the devitrified glass is very poor in rees light rare earth elements lrees and deficits in eu and yban ultrarefractory pattern the genetic models suggested so far cannot explain what is observed and consequently we offer a new model for silicate inclusion formation in iie and related irons nebular processes and a relationship with e meteorites guin or ca al rich inclusions cais kodaikanal are indicated a sequence of condensation cas tin or refractory pyroxene rich liquids and vapor solid elemental exchange can be identified that took place beginning under reducing and ending at oxidizing conditions phosphate rutile formation alkali and fe 2 metasomatism metasomatic loss of rees from glasses

three dimensional geometry and tectonostratigraphy of the pennine zone central alps switzerland and northern italy abstract continental collision during alpine orogenesis entailed a polyphase deformation history d1 d5 in the pennine zone of the central alps the regional tectonostratigraphy was basically developed during d1 and d2 characterised by isoclinal typically north closing recumbent anticlines separated by pinched in synclines on the scale of tens of kilometres later deformation phases d3 and d4 warped the stack into wavy to open folds exhumation of this zone resulted locally in later vertical shortening and folding of already steep fabrics d5 three dimensional models of the nappe pile were constructed based on geostatistical assessment of the regional foliation field and considering the abundant structural field data these models indicate the existence of five principal tectonostratigraphic levels developed during d1 and thus equivalent to nappe units s str the gotthard the leventina antigorio the maggia simano and probably the monte leone as well as the composite lepontine series lebendun soja and adula cima lunga levels all these tectonic units formed part of the passive continental margin of europe prior to the onset of the alpine orogenesis individual isoclinal post nappe folds reflect relative displacements on the order of 40 km or more the most prominent d2 post nappe structure is the wandfluhhorn fold structurally equivalent to the northern closure of the leventina lucomagno antiform the lebendun and monte leone folds are of similar magnitudes and also affect the whole nappe pile whereas the smaller mogno and molare synforms only refold the maggia simano nappe internally principal d3 and d4 structures are the tight mergoscia synform directly north of the insubric fault between bellinzona and locarno southern steep belt the maggia steep zone forming the steep western limb of the campo tencia synform and subdividing the lepontine dome into the simplon and ticino subdomes the chiera synform steepening the dominant foliation in the north northern steep belt and the vanzone and claro antiforms steepening the dominant foliation in the south southern steep belt the current geometry of the northern and southern steep belts reflects an interplay between d4 and d3 involving both fold interference and reactivation tightening

clinopyroxene ree distribution coefficients for shergottites the ree content of the shergotty melt abstract ree distribution coefficients were measured between synthetic pyroxenes and melts similar in composition to the inferred shergotty intercumulus liquid by in situ analysis with the electron microprobe using samples doped to per cent concentration levels these coefficients exhibit a strong positive correlation with pyroxene wollastonite content recommended values for augites similar in composition to the shergotty cumulus augite cores wo32en48 are d la 0 023 d ce 0 039 d nd 0 10 d sm 0 17 d eu 0 16 d gd 0 20 d yb 0 29 and d lu 0 30 recommended values for pigeonites similar in composition to the shergotty cumulus pigeonite cores wo12en58 are d la 0 002 d ce 0 004 d nd 0 019 d sm 0 031 d yb 0 13 and d lu 0 13 these values resemble distribution coefficients measured for terrestrial basalts of higher mg fe than the shergotty melt rather than those of more evolved siliceous rocks of similar mg fe to the shergotty melt thus it appears that mg fe is considerably less important than other factors in determining distribution coefficient values for pyroxenes ree abundances were computed for the shergotty intercumulus melt using distribution coefficients measured for the natural phase compositions these computed abundances display lree depletion such lree depleted abundance patterns cannot be generated by simple partial melting of a mafic mineral assemblage having the lree enriched patterns required for a two stage sm nd evolution history this result implies that either 1 the melting process was complex e g continuous melting 2 the source region had a more complex history than that of the simple 2 stage model or 3 shergotty does not satisfy the closed system assumption of the calculation and has suffered post magmatic lree enrichment

changes in environment over the last 800 000 years from chemical analysis of the epica dome c ice core the epica ice core from dome c extends 3259 m in depth and encompasses 800 ka of datable and sequential ice numerous chemical species have been measured along the length of the cores here we concentrate on interpreting the main low resolution patterns of major ions we extend the published record for non sea salt calcium sea salt sodium and non sea salt sulfate flux to 800 ka the non sea salt calcium record confirms that terrestrial dust originating from south america closely mirrored antarctic climate both at orbital and millennial timescales a major cause of the main trends is most likely climate in southern south america which could be sensitive to subtle changes in atmospheric circulation sea salt sodium also follows temperature but with a threshold at low temperature we re examine the use of sodium as a sea ice proxy concluding that it is probably reflecting extent with high salt concentrations reflecting larger ice extents with this interpretation the sodium flux record indicates low ice extent operating as an amplifier in warm interglacials non sea salt sulfate flux is almost constant along the core confirming the lack of change in marine productivity for sulfur producing organisms in the areas of the southern ocean contributing to the flux at dome c for the first time we also present long records of reversible species such as nitrate and chloride and show that the pattern of post depositional losses described for shallower ice is maintained in older ice it appears possible to use these concentrations to constrain snow accumulation rates in interglacial ice at this site and the results suggest a possible correction to accumulation rates in one early interglacial taken together the chemistry records offer a number of constraints on the way the earth system combined to give the major climate fluctuations of the late quaternary period

geochemistry and genesis of the lengenbach pb zn as tl ba mineralisation binn valley switzerland the lengenbach pb zn as tl ba mineralisation is located in triassic dolostones of the penninic zone in the swiss alps where alpine metamorphism reached upper greenschist to lower amphibolite grade geochemical data are used to constrain the origin of this unique occurrence two metamorphic redox environments are present the as iii rich zone is controlled by barite pyrite while the reduced zone contains graphite or pyrrhotitepyrite and formally zerovalent as the as iii rich zone is characterised by a mineral assemblage consistent withfo2 in the stability field of barite pyrite an as pb tl rich sulphide melt coexisted with a hydrothermal fluid at 300 c in this zone mineralised dolostones are anomalous in as pb ag tl hg zn ba cd fe cu mo u v b ga cr and possibly sri and au in order of decreasing enrichment as pb and zn are present in the 0 1 to 1 range tl and ag reach several hundred ppm uraninite is concentrated in silicate rich bands and yields a late alpine u pb age of 18 5 0 5 ma pb and s isotopic variations are interpreted by metamorphic overprinting and re equilibration within an isochemically metamorphosed mineralisation hydrothermal sulphides are more strongly affected by uranogenic pb than massive pb as sulphides representing a former sulphide melt the least overprinted mineralisation is characterised by206pb 204pb 18 44 18 56 207pb 204pb 15 60 15 75 208pb 204pb 38 44 38 84 and 34s sulphide 25 2 s isotopic variations are largely a result of sulphide sulphate re equilibration yielding temperatures of 450 30 c 87sr 86sr ratios of mineralised samples are lower than or equal to host dolostones precluding major infiltration of basement derived fluids during alpine metamorphism the sr source 87sr 86sr close to 0 708 probably was seawater with a radiogenic detrital mineral component the genesis of the unique lengenbach mineralisation is interpreted as the result of isochemical metamorphic overprinting of a carbonate hosted stratiform sulphide mineralisation well crystallised sulphide minerals in fissures and druses formed during retrograde cooling of a sulphide melt in equilibrium with a hydrothermal fluid the primary mineralisation was probably formed at or close below the sea floor and fed by sulphide poor hydrothermal fluids sulphide was largely derived from seawater by open system bacterial sulphate reduction u v and mo may be seawater derived

first finding of impact melt in the iie netschaevo meteorite about half of the iie nonmagmatic iron meteorites contain silicate inclusions with a primitive to differentiated nature the presence of preserved chondrules has been reported for two iie meteorites so far netschaevo and mont dieu which represent the most primitive silicate material within this group in this study silicate inclusions from two samples of netschaevo were examined both silicate inclusions are characterized by a porphyritic texture dominated by clusters of coarse grained olivine and pyroxene set in a fine grained groundmass that consists of new crystals of olivine and a glassy appearing matrix this texture does not correspond to the description of the previously examined pieces of netschaevo which consist of primitive chondrule bearing angular clasts detailed petrographic observations and geochemical analyses suggest that the investigated samples of netschaevo consist of quenched impact melt this implies that netschaevo is a breccia containing metamorphosed and impact melt rock imr clasts and that collisions played a major role in the formation of the iie group