interior of the moon the presence of garnet in the primitive deep lunar mantle new trace element data have been generated by inductively coupled plasma mass spectrometry icp ms for 65 high and low ti mare basalts from the apollo 11 12 14 15 and 17 landing sites these data demonstrate that ratios of the high field strength elements and yttrium are generally chondritic in the mare source regions for the low ti basalts but nonchondritic in the high ti basalts and potassium rare earth elements and phosphorus kreep such differences can be explained by addition and subtraction respectively of ilmenite this interpretation is consistent with derivation of the basalts from lunar magma ocean lmo cumulates through which late stage ilmenite has sunk and mixed with earlier magma ocean products compositional differences between the mare basalts and volcanic glass beads suggest that at least some of the latter were derived from a garnet bearing source region siderophile and chalcophile element data suggest that the garnet bearing source escaped the lmo melting event and thus represents primitive moon material the remaining glasses are generally very low ti vlt and appear to have been derived from early lmo cumulates i e olivine and orthopyroxene similar to the vlt basalts the remaining glasses were derived from below the lmo cumulates and as the magmas rose they underwent sequential assimilation to varying degrees initially of an ilmenite rich cumulate followed by a kreep component this study presents geochemical evidence for the existence of garnet in a mare source and demonstrates the likelihood that the lmo was not whole moon thus preserving primitive lunar material which has acted as the source region for at least some of the volcanic glasses

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

optically continuous silcrete quartz cements of the st peter sandstone high precision oxygen isotope analysis by ion microprobe a detailed oxygen isotope study of detrital quartz and authigenic quartz overgrowths from shallowly buried 1 km quartz arenites of the st peter sandstone in sw wisconsin constrains temperature and fluid sources during diagenesis quartz overgrowths are syntaxial optically continuous and show complex luminescent zonation by cathodoluminescence detrital quartz grains were separated from 53 rocks and analyzed for oxygen isotope ratio by laser fluorination resulting

geothermometry from brine analyses lessons from the gulf coast u s a abstract geothermometers based on mineral water equilibria are of limited use at temperatures characteristic of hydrocarbon production from sedimentary basins metastable detrital phases such as alkali feldspars and plagioclase persist to temperatures characteristic of the deepest wells sasmpled approaching 200 c and equilibria involving stable phases such as albite illite and quartz are not commonly achieved empirical relations such as that between mg and li are more successful in predicting subsurface formation water temperatures than are equilibrium relations involving quartz carbonates or feldspars the concentrations of most components in saline formation waters seem to be governed by kinetic rather than by equilibrium considerations

elemental and isotopic abundances of lithium in chondrule constituents in the allende meteorite abstract elemental and isotopic abundances of lithium in chondrule constituents in the allende cv3 meteorite were determined using secondary ion mass spectrometry olivines and mesostasis dominated by a feldspathic phase are depleted in li 1 g g 1 and 0 1 0 6 g g 1 respectively in contrast low ca pyroxenes and mesostasis dominated by a na rich phase are enriched in li 1 8 g g 1 and 0 4 3 5 g g 1 respectively and the interchondrule matrix is generally enriched in li 2 0 g g 1 on average the li isotopic abundance of olivine ranges from 7 li 32 to 21 the spatial distributions of elemental and isotopic abundances of li in olivines within individual chondrules exhibit no systematic pattern this suggests that the distribution of li in olivine was not disturbed during aqueous alteration or thermal metamorphism on the allende meteorite parent body although mesostasis is the last crystallizing phase from a chondrule melt and is expected to be enriched in li in the allende meteorite it is generally depleted in li we suggest that during aqueous alteration on the cv asteroid li in mesostasis was leached out by aqueous fluids the li enriched na rich mesostasis was probably produced later by infiltration of na rich fluids it seems likely that aqueous fluids sequestered alkali elements from the allende chondrite region in the cv parent asteroid although significant amounts of li are preserved in ferrous olivine in the interchondrule matrix

oxygen isotope evidence for rapid mixing of the hed meteorite parent body abstract the 16 o 17 o and 18 o abundances of howardites eucrites and diogenites have been used to assign them to a single hed parent body thought to be asteroid 4 vesta we report the first evidence of oxygen isotopic heterogeneity among hed meteorites indicating incompletely mixed sources new high precision oxygen isotope measurements of 34 hed meteorites reveal that most have the same 17 o consistent with a very rapid early history of large scale mixing on vesta however howardites are on average very slightly enriched in 16 o whereas ibitira caldera pasamonte and alha78132 are 16 o depleted compared to other investigated eucrites the 17 o of ibitira is completely different from all other heds measured some of the results for eucrites and diogenites can be explained by partial melting and rapid mixing of the interior of vesta others require a separate parent body or indicate that parts of the outer layer of vesta retained some primary isotopic heterogeneity the oxygen isotopic composition of howardites provides an upper limit for the amount of admixed carbonaceous chondritic material into the hed parent body regolith

lithium isotopes in global mid ocean ridge basalts abstract the lithium isotope compositions of 30 well characterized samples of glassy lavas from the three major mid ocean ridge segments of the world spanning a wide range in radiogenic isotope and elemental content and sea floor physical parameters have been measured the overall data set shows a significant range in 7li 1 6 to 5 6 with no global correlation between li isotopes and other geochemical or tectonic parameters the samples with the greatest lithophile element depletion n morb k2o tio2

lithium isotopes as indicators of meteorite parent body alteration hydrothermal processing on planetesimals in the early solar system produced new mineral phases including those generated by the transformation of anhydrous silicates into their hydrated counterparts carbonaceous chondrites represent tangible remnants of such alteration products lithium isotopes are known to be responsive to aqueous alteration yet previously recognized variability within whole rock samples from the same meteorite appears to complicate the use of these isotopes as indicators of processing by water we demonstrate a new way to use lithium isotopes that reflects aqueous alteration in carbonaceous chondrites temperature appears to exert a control on the production of acetic acid soluble phases such as carbonates and poorly crystalline fe oxyhydroxides temperature and degree of water rock interaction determines the amount of lithium isotope fractionation expressed as the difference between whole rock and acetic acid leachable fractions using these features the type 1 chondrite orgueil 7li whole rock 4 3 7li acetic whole 1 2 can be distinguished from the type 2 chondrites murchison 7li whole rock 3 8 7li acetic whole 8 8 and carbonate poor tagish lake 7li whole rock 4 3 7li acetic whole 9 4 this initial study suggests that lithium isotopes have the potential to reveal the role of liquid water in the early solar system

criteria for recognition of localization and timing of multiple events of hydrothermal alteration in sandstones illustrated by petrographic fluid inclusion and isotopic analysis of the tera group northern spain stratigraphic relations detailed petrography microthermometry of fluid inclusions and fine scale isotopic analysis of diagenetic phases indicate a complex thermal history in tithonian fluvial sandstones and lacustrine limestones of the tera group north spain two different thermal events have been recognized and characterized which are likely associated with hydrothermal events that affected the cameros basin during the mid cretaceous and the eocene multiple stages of quartz cementation were identified using scanning electron microscope cathodoluminescence on sandstones and fracture fills primary fluid inclusions reveal homogenization temperatures th from 195 to 350 c in the quartz cements of extensional fracture fillings the high variability of th data in each particular fluid inclusion assemblage is related to natural reequilibration of the fluid inclusions probably due to cretaceous hydrothermal metamorphism some secondary fluid inclusion assemblages show very consistent data th 281 305 c and are considered not to have reequilibrated they are likely related to an eocene hydrothermal event or to a retrograde stage of the cretaceous hydrothermalism this approach shows how multiple thermal events can be discriminated a very steep thermal gradient of 97 214 c km can be deduced from 18o values of ferroan calcites 18o 14 2 11 8 v pdb that postdate quartz cements in fracture fillings furthermore illite crystallinity data anchizone epizone boundary are out of equilibrium with high fluid inclusion th these observations are consistent with heat flux related to short lived events of hydrothermal alteration focused by permeability contrasts rather than to regional heat flux associated with dynamo thermal metamorphism these results illustrate how thermal data from fracture systems can yield thermal histories markedly different from host rock values a finding indicative of hydrothermal fluid flow

late accretion as a natural consequence of planetary growth the mantles of the terrestrial planets contain elemental abundances that suggest accretion continued at a late stage after core formation geochemical data of meteorites from differentiated asteroids are consistent with such a late accretion event suggesting that the phenomenon occurred throughout the solar system and was related to planet formation

widespread magma oceans on asteroidal bodies in the early solar system our solar system formed about 4 6 billion years ago and within 4 million years small planetary bodies had formed some melting to form volcanic and related rocks two families of meteorites the heds and angrites are thought to have originated from asteroids that melted at this time new oxygen isotope measurements confirm that these meteorites are from two distinct asteroids that underwent large scale melting in the early solar system these new results show that early global scale melting was a feature of all the differentiated planets earth moon and mars and asteroids so far sampled immediately following the formation of the solar system small planetary bodies accreted1 some of which melted to produce igneous rocks2 3 over a longer timescale 15 33 myr the inner planets grew by incorporation of these smaller objects4 5 through collisions processes operating on such asteroids strongly influenced the final composition of these planets4 including earth5 currently there is little agreement about the nature of asteroidal igneous activity proposals range from small scale melting to near total fusion and the formation of deep magma oceans2 here we report a study of oxygen isotopes in two basaltic meteorite suites the heds howardites eucrites and diogenites which are thought to sample the asteroid 4 vesta6 and the angrites from an unidentified asteroidal source our results demonstrate that these meteorite suites formed during early global scale melting 50 per cent events we show that magma oceans were present on all the differentiated solar system bodies so far sampled magma oceans produced compositionally layered planetesimals the modification of such bodies before incorporation into larger objects can explain some anomalous planetary features such as earth s high mg si ratio

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

driving forces for the weathering and alteration of silica in the regolith implications for studies of prehistoric flint tools a range of geochemical and mineralogical factors trigger the weathering and influence the stability of various silica phases under near surface temperatures and pressures based on the current knowledge of the crystallochemical basis of silica behaviour in near surface environments the mineralogical and petrographical transformations of silica under weathering conditions in the regolith are reviewed using data from wide ranging and detailed investigations of siliceous materials some of the investigations are of siliceous materials that evolved in near surface environments over geological time and thus the weathering and alteration features are relatively clear and well expressed examples include weathering of tightly cemented sandstones the formation of silica duricrusts pedogenetic silcretes and the weathering of flints the various micromorphological and mineralogical forms of silica as determined by high resolution petrographic and electron optical techniques can be related to geochemical and hydrological conditions in particular microenvironments however new studies have demonstrated that silica alteration and transformation mechanisms can also occur within prehistoric and historic time intervals these are also described but are more difficult to observe principally because of the microcrystalline character of the alteration phases and the infra millimetric scale on which they develop of many potential applications of knowledge about the near surface alteration of silica in regolith materials and the environmental conditions under which it occurs our studies can be used as a basis determining the provenance and post discard history of prehistoric flint tools and artefacts in part to determine the source of the primary raw material we suggest that the mineralogical and petrographical characteristics of the weathering rind cortex of the flint specifically the recrystallization dissolution and deposition of the silica phases and the spatial arrangement of surfaces that have undergone successive transformations are related to specific and identifiable weathering environments

labile trace elements in basaltic achondrites can they distinguish between meteorites from the moon mars and v type asteroids we report data for 14 mainly labile trace elements ag au bi cd cs ga in rb sb se te tl u and zn in eight whole rock lunar meteorites asuka a 881757 dar al gani dag 262 elephant moraine eet 87521 queen alexandra range que 93069 que 94269 que 94281 yamato y 793169 and y 981031 and martian meteorite dag 476 and incorporate these into a comparative study of basaltic meteorites from the moon mars and v type asteroids multivariate cluster analysis of data for these elements in 14 lunar 13 martian and 34 howardite eucrite and diogenite hed meteorites demonstrate that materials from these three parents are distinguishable using these markers of late low temperature episodes this distinguishability is essentially as complete as that based on markers of high temperature igneous processes concentrations of these elements in 14 lunar meteorites are essentially lognormally distributed and generally more homogeneous than in martian and hed meteorites mean siderophile and labile element concentrations in the 14 lunar meteorites indicate the presence of a ci equivalent micrometeorite admixture of 2 6 when only feldspathic samples are considered our data show a slightly higher value of 3 4 consistent with an increasing micrometeorite content in regolith samples of higher maturity concentrations of labile elements in the 8 feldspathic samples hint at the presence of a fractionated highly labile element component possibly volcanic in origin at a level comparable to the micrometeorite component apparently the process es that contributed to establishing lunar meteorite siderophile and labile trace element contents occurred in a system open to highly labile element transport

authigenic quartz microfabrics in cretaceous turbidites evidence for silica transformation processes in sandstones abstract lower cretaceous sandstone turbidites in the scapa field north sea contain a complex variety of authigenic quartz microfabrics early diagenetic microfabrics predate burial calcite cements and compaction they comprise abundant grain rimming microquartz intergranular aggregates of microquartz with authigenic illite smectite and localized isopachous cryptocrystalline quartz and chalcedonite fringes these precipitates contain evidence of precursor opal ct in the form of dissolved recrystallized or pseudomorphed lepispheres and rim cements late diagenetic quartz microfabrics are postcompactional and either replace or overgrow burial calcite cements they display a paragenetic trend from microporous fibrous silica quartzine or chalcedonite to equant syntaxial and mosaic meso uartz cements none of these contain evidence for opal ct precursors and they are likely to have precipitated directly from silica rich pore fluids cathodoluminescence examination of calcite cemented sandstone intervals reveals that siliceous sponge spicules were a major depositional component and were the most likely silica source for opal ct and subsequent quartz cementation dissolution of biogenic silica and formation of opal ct began shortly after deposition with replacement of opal ct by quartz during burial of the scapa member to 1 2 km the early diagenetic silica transformations are identical to those recorded from cenozoic porcelanites and cherts thermodynamic models developed for the diagenesis of biogenic cherts can therefore be applied to the scapa sandstones and qualitatively explain the development of contrasting quartz microfabrics on a bed to bed or smaller scale in contrast direct precipitation of chalce onic quartz during late diagenesis required a resurgence of high supersaturations this is difficult to account for without some import of silica to the sandstones and or cooling of pore fluids precipitation most probably occurred from allochthonous deep basinal brines associated with early stages of hydrocarbon migration

history of diagenetic fluids in a distant foreland area middle and upper pennsylvanian cherokee basin kansas usa fluid inclusion evidence abstract analysis of fluid inclusion data in diagenetic cements from pennsylvanian limestones and sandstones of the cherokee basin in southeastern kansas reveals the succession of diagenetic fluids in a distant foreland of the arkoma ouachita system this succession includes early low salinity 0 0 2 4 wt nacl eq fluids of meteoric affinity fluid i followed by low temperature na ca cl brines fluid ii with salinities between 8 4 and 24 1 wt nacl eq fluids i and ii were present in the system during precipitation of early stage calcite cements at temperatures less than about 50 c another na ca cl brine fluid iii with salinity up to 25 wt nacl eq was present in the system later at temperatures of maximum burial at least 80 85 c and higher fluid iii is followed by a na cl brine fluid iv with salinities about 19 21 wt nacl eq characterized by temperatures distinctly higher than maximum burial up to 150 c fluid iii and fluid iv were entrapped during precipitation of late stage baroque dolomite and fe dolomite in pennsylvanian limestones and late stage fe dolomite and ankerite in pennsylvanian sandstones the record of progression from fluid iii to fluid iv may have been partially obscured by thermal re equilibriation of some inclusions during migration of fluid iv fluids with na ca cl chemistry fluid ii and iii were either indigenous subsurface fluids of the cherokee and arkoma basins or might have originated as reflux fluids in a permian evaporitic basin of central kansas later na cl brine fluid iv originated in deeper parts of the arkoma ouachita system and might have acquired their salinity by dissolution of hypothetical salts buried beneath the ouachitas temperatures recorded by fluid inclusions in late diagenetic carbonates are 20 60 c higher than those calculated for the maximum burial of the studied section this thermal anomaly suggests an advective heat transfer from the arkoma ouachita system onto the shelf of the cherokee basin related to the invasion of late diagenetic fluids

ion microprobe analysis of 18o 16o in authigenic and detrital quartz in the st peter sandstone michigan basin and wisconsin arch usa contrasting diagenetic histories abstract the oxygen isotopic compositions of authigenic quartz cements in sandstones provide a monitor of the temperatures compositions and origins of pore occluding fluids during diagenesis but quartz overgrowths are too fine grained to be amenable to conventional isotopic analysis we have used a cameca ims 4f ion microprobe to determine oxygen isotopic variations in authigenic and detrital quartz in four samples of the ordovician st peter sandstone from the michigan basin and wisconsin arch midwestern usa ion microprobe isotopic analyses have been successfully accomplished with an internal precision of 1 1 and a spatial resolution of 20 30 m at low mass resolution using a high voltage offset technique repeated analyses of the quartz standard demonstrate a reproducibility of close to 1 1 sd in good agreement with that expected from counting statistics the four ion probe samples were chosen as representative of thirteen samples that were mechanically and chemically disaggregated sieved and analysed as a function of sieve size by conventional bulk mineral techniques conventional and ion microprobe analyses are mutually consistent supporting the accuracy of the ion microprobe analyses within sample isotopic variations of up to 13 and micro scale isotopic variations of at least 4 over a distance of 100 m have been measured within quartz overgrowths in a sandstone from the wisconsin arch overgrowths are uniformly higher in 18o than detrital grains and gradients of up to 25 exist across a few microns 18o enriched quartz overgrowths in sandstones from the wisconsin arch show complex cl zonation and reflect one of two possible processes 1 low temperature quartz precipitation during mixing of meteoric waters with upwelling basinal fluids 2 higher temperature quartz precipitation during episodic gravity driven upwelling of warm basinal fluids of comparable isotopic composition to michigan basin fluids from the illinois basin related to evolution of mississippi valley type pb zn ore forming fluids quartz overgrowths in michigan basin sandstones which derived their silica locally by pressure solution are thought to have precipitated continuously over a range of temperatures from hot basinal fluids of restricted isotopic composition and circulation detrital quartz shows significant intea grain and intergrain isotopic variation 5 13 but no significant inter sample variation consistent with a uniform source of granitoid and metamorphic quartz in space and time

origin of howardites diogenites and eucrites a mass balance constraint abstract howardite meteorites are regolith breccias impact produced mixtures that consist of two main rock types basalts that strongly resemble eucrite meteorites and pyroxene cumulates that strongly resemble diogenite meteorites there are basically two petrogenetic models for the noncumulate basaltic parts of howardites 1 1 genesis as residual liquids of the same magma s that had earlier crystallized the pyroxene cumulates and 2 2 genesis as primary unmodified partial melts from the interior of the parent asteroid a mass balance constraint based on al indicates that unless the ratio degree of melting during genesis of melts parental to pyroxene cumulates degree of melting during genesis of primary basalts was on average greater than about 2 8 a scenario that implies an implausible bimodality of degree of melting on the howardite parent body an average howardite must contain more residual liquid basalt than primary basalt if as seems likely eucrites per se are identical to the howardite basaltic components and diogenites per se are the pyroxene cumulate components then more than half of the eucrites probably formed from residual liquids of magmas that had earlier produced the diogenites considering all the potential complexities of petrpgenesis on the howardite parent body neither the partial melting model nor the fractional crystallization residual liquid model is likely correct for all noncumulate eucrites

lithium isotope fractionation during continental weathering processes a comprehensive understanding of lithium isotope fractionation during terrestrial weathering is necessary in order to use lithium isotopes to trace chemical cycles climatic changes and igneous processes this study investigates lithium isotope fractionation in two laboratory experiments and by analyses of natural basalt weathering products partial dissolution of basalts in the laboratory does not result in fractionation of lithium isotopes but similar dissolution of a granite sample causes significant fractionation this may reflect dissolution of secondary minerals from the granite or differences in the li isotope composition of primary minerals in this more evolved igneous rock significant li isotope fractionation was also observed during sorption onto mineral surfaces in the laboratory although this was highly dependent on sample mineralogy no fractionation accompanies the outer sphere physisorption of li to smectite surfaces some fractionation accompanies sorption onto ferrihydrite and significant fractionation with 0 986 is seen during inner sphere chemisorption to gibbsite surfaces repeat experiments with varying amounts of sorption demonstrate that li remains in an exchangeable site on the gibbsite surface the extent of fractionation onto gibbsite observed in this study 13 is about half that required in order for clay surface removal to balance the ocean li isotope budget isotopic fractionation of li was found to occur on a 300 yr timescale in both cold and warm natural environments a minimally altered rock surface from iceland was found to be two lighter in 7li than the sample interior probably due to the preferential incorporation of 6li in clay or oxide rich alteration products on the sample surface soil samples from hawaii also demonstrate li fractionation during weathering in this environment rainwater 7li 10 contributes a significant flux of isotopically heavy li to the developing soil despite this soils have similar li isotope compositions to the primary basalt 7li 4 indicating that 6li is preferentially retained during weathering this conclusion is supported by isotopically heavy river water on hawaii 7li 22 and by the correlation between li concentration and 7li in the soil the lab and field based measurements of this study clearly demonstrate that lithium fractionates during weathering potentially providing information about the weathering environment now and in the past

the age of the solar system redefined by the oldest pb pb age of a meteoritic inclusion the age of the solar system is defined by the formation of the first solid grains in the solar nebula pb pb age dating of these solids which were later trapped in a meteorite indicates that the solar system is 0 34 1 91 million years older than previously thought the age of the solar system can be defined as the time of formation of the first solid grains in the nebular disc surrounding the proto sun this age is estimated by dating calcium aluminium rich inclusions in meteorites these inclusions are considered as the earliest formed solids in the solar nebula their formation marks the beginning for several long and short lived radiogenic clocks that are used to precisely define the timescales of solar system events such as the formation and evolution of planetary bodies1 2 3 here we present the 207pb 206pb isotope systematics in a calcium aluminium rich inclusion from the northwest africa 2364 cv3 group chondritic meteorite which indicate that the inclusion formed 4 568 2 million years ago this age is between 0 3 refs 4 5 and 1 9 refs 1 6 million years older than previous estimates and is the oldest age obtained for any solar system object so far we also determined the 26al 26mg model age of this inclusion and find that it is identical to its absolute pb pb age implying that the short lived radionuclide 26al was homogeneously distributed in the nebular disc surrounding the proto sun from the consistently old ages in the studied inclusion we conclude that the proto sun and the nebular disc formed earlier than previously thought

downwelling longwave flux over summit greenland 2010 2012 analysis of surface based observations and evaluation of era interim using wavelets this study analyzes the downwelling longwave radiation dlw over the greenland ice sheet gris using surface based observations from summit station 72 n 38 w 3210 m and the european centre for medium range weather forecasts interim reanalysis era interim dlw fields since surface based observations are sparse in the arctic the accuracy of including reanalyses for spatial context is assessed first the dlw at summit is reported including the significant time scales of variability using time frequency decomposition wavelet analysis a new method for evaluating reanalyses is then introduced that also uses wavelet analysis era interim dlw performs reasonably well at summit but because it includes too many thin clouds and too few thick clouds it is biased low overall the correlation between the observations and era interim drops from r2 0 8 to near 0 for time series reconstructed from time scales less than 4 days these low correlations and additional analyses suggest that the spatial resolution of the data sets is a factor in representing variability on short time scales the bias is low across all time scales and is thus likely tied to cloud generation processes in the model rather than the spatial representation of the atmosphere across the gris the exception is autumn when era interim overestimates the influence of clouds at time scales of 1 and 4 weeks the spatial distribution of cloud influence on the dlw across the gris indicates that summit is located in a transition zone with respect to cloud properties the gradient across this transition zone is steepest near summit in autumn so the spatial characteristics of the atmosphere near summit may contribute to the era interim bias during this time

facies related diagenesis and multiphase siderite cementation and dissolution in the reservoir sandstones of the khatatba formation egypt s western desert in the fluvio deltaic quartz arenitic sandstones of the jurassic khatatba formation in the salam field egypt9s western desert diagenesis and sedimentary facies control reservoir quality fluvial channel sandstones have the highest porosities 10 15 and permeabilities 100 600 md in part because of siderite cementation which 1 inhibited compaction and quartz cement and 2 was later dissolved creating intergranular secondary porosity 1 4 of total porosity fluvial crevasse splay and marine sandstones have the lowest reservoir quality because of an abundance of depositional kaolin matrix and pervasive shallow burial fe dolomite cement respectively siderite precipitation was multiphase and separated by distinct dissolution events the earliest siderite precipitated near surface within suboxic tropical coastal swamps containing predominantly meteoric waters some influence of marine waters is indicated by local enrichments in mg and ca the next major siderite generation shows a trend to decreasing mn and ca contents and is of shallow burial origin the last major siderite phase is mg rich and interpreted as deeper burial in origin some dissolution occurred during shallow burial related to climatically controlled meteoric water fluxing under unconformities the most important dissolution however occurred during deep burial resulting in 1 a major corrosion surface predating the last mg rich zone 2 selective dissolution of some earlier zones and 3 secondary porosity this burial dissolution is interpreted to have been caused by cooling of compactional waters expelled from the basin along major faults other diagenetic phases observed include early diagenetic pyrite kaolin quartz bitumen and late diagenetic barite and illite kaolinite precipitated at shallow depths 130 c during and or after rapid late cretaceous burial quartz developed in two phases separated by oil migration this paper illustrates that in fluvio deltaic quartz arenites deposited under the influence of humid tropical climate reservoir quality can be largely controlled by the contrasting pathways of carbonate diagenesis followed by the different sedimentary facies this paper also documents a case in which siderite dissolution generated significant secondary porosity in reservoir sandstones and where both siderite cementation and dissolution took place in multiple phases during different diagenetic stages including early shallow burial and deep burial diagenesis the present study also shows that in multiphase siderite cements the earlier growth zones can be selectively dissolved and replaced by later siderite zones i e recrystallized during burial diagenesis these findings contrast with the general thought that siderite cements are not susceptible to generation of significant secondary porosity by dissolution and that earlier formed siderites are essentially stable during diagenesis

silica recrystallization in petrified wood abstract the mineralogy of thirty three samples of silicified wood was examined by x ray diffraction and each sample was found to consist of one of the following opal a opal ct or quartz the correlation between ordering of the silica phases and sample age suggests that the opal a opal ct quartz conversion sequence occurs in much the same manner and at approximately the same rates as in biogenic siliceous marine sediments in addition a poorly crystalline clay phase illite was identified in most of these samples groundwater leaching of volcanogenic sediments commonly thought to be the silica source may also provide aluminum and other cations that are deposited simultaneously in wood tissue consequently silica recrystallization may be accompanied by authigenic clay formation

fluid rock interaction history during stabilization of early dolomites upper knox group lower ordovician u s appalachians abstract the lower ordovician upper knox group is characterized by shallowing upward peritidal cycles that are extensively dolomitized to form massive dolomite most 85 replacive dolomite is stratigraphically controlled composed of very fine to medium crystalline planar to nonplanar early dolomite composed of zones 1 2 and 3 dolomites remaining dolomite occurs as medium to coarsely crystalline nonplanar late replacive dolomite zones 2 and 3 late dolomites that selectively replaces limestone associated with stylolites and fractures or forms massive dolomite fronts complexly zoned zone 2 to 6 saddle dolomite cements make up less than 5 of all dolomite and primarily fill solution voids and fractures early dolomites are near stoichiometric and relative to early ordovician marin carbonates are similar to or significantly depleted in 18o and sr slightly to significantly enriched in mn and fe and have similar 87sr 86sr values relative to early dolomites late zones 2 and 3 dolomites are depleted in 18o and st enriched in mn and fe and have similar 87sr 86sr values early dolomites are interpreted to have formed from modified seawater during seaward progradation of tidal flats within each high frequency fifth and fourth order cycle duration late dolomites based on their texture and geochemistry formed as a result of recrystallization of early dolomites as direct replacement of limestone at elevated temperatures and as cement in fractures and secondary solution voids covariant trends between textures and geochemical compositions for early dolomite indicate that presentday compositions of knox early dolomite record a history of progressive diagenetic modification stabilization or recrystallization involving varying degrees of changes of textural and geochemical compositions during multiple episodes of dolomitization early dolomites wit the most extensively altered textures are more stoichiometric more depleted in 18o and sr and more enriched in mn and fe relative to texturally less altered early dolomite initial stabilization may have occurred syndepositionally in modified seawater continued stabilization of early dolomite likely occurred in fresh or mixed waters of a middle ordovician meteoric aquifer associated with knox unconformity development final stabilization occurred by deep burial brines at elevated temperatures as indicated by 1 extensive replacement and overgrowth of early dolomite by late dolomites 2 a progressive increase in crystal size and abundance of nonplanar crystal boundaries with increase in replacement by late dolomites and 3 the similarity of the geochemical compositions of texturally most extensively altered early dolomites and late dolomites

silica diagenesis i solubility controls abstract the diagenetic sequence of silica is examined in terms of several thermodynamic and kinetic concepts the relationship between solubility and surface area or particle size is sufficient to explain simple opal a opal ct quartz transformations suggesting that the role of temperature and other physical parameters may not be as critical as previously thought complexation and adsorption in an impure system when added to the model allow for possibilities of opal a transformation directly to quartz of clay and zeolite formation from an opaline silica source and of variations in silica transformation rates due to presence of impurities in the system

magnesian calcite cements and their diagenesis dissolution and dolomitization mururoa atoll the most ubiquitous syn sedimentary cements affecting mururoa atoll are composed of magnesian calcite three main types are distinguished fibrous bladed and sparitic on the basis of petrography morphology and mgco3 concentration of the constituting crystals while peloid infills a particular form of hmc chemical precipitation also exist petrographic evidence and isotopic signatures are compatible with marine precipitation mururoa atoll was exposed several times to meteoric diagenesis resulting in varied diagenetic alterations including selective dissolution and partial dolomitization of mg calcite cements these alterations are responsible for substantial modifications of the initial cement fabrics and may introduce unconformities in the diagenetic chronology the first stage of the partial dissolution of mg calcite induces the development of chalky white friable zones within the initially crystalline hard cement layers at ultrascale this is due to the creation of micro voids along the elongate cement fibres advanced dissolution includes total disappearance of cement portions as attested to by large voids within the cement crust and or between superposed cement layers mg calcite dissolution is related to meteoric diagenesis during periods of quaternary exposure the creation of voids within mg calcite layers is due to the mechanical removal of previously altered calcium carbonate a process suggesting marine or non marine water flow probably in the vadose environment selective dolomitization of mururoa cements involves alternations of calcite and dolomite which form successive cement like rinds within primary cavities at mururoa these alternations are the result of selective dolomitization of the pre existing mg calcite cements rather than successive precipitation of calcite and dolomite selective dolomitization of mg calcite cements at mururoa indicates that a given cement succession is not necessarily a simple chronological sequence oxygen isotope values of dolomites are enriched in 186 by about 3 pdb within calcite dolomite pseudo alternations the dolomitizing fluid at mururoa seems similar to present marine water although some mixture with meteoric water is probable to favour dissolution associated with dolomitization

implications of trace element composition of syntaxial quartz cements for the geochemical conditions during quartz precipitation in sandstones a petrographic investigation revealed polyphase quartz cementation in the finefrau sandstone upper carboniferous western germany and the solling sandstone lower triassic central germany three different cements could be distinguished in each sandstone based on their cathodoluminescence and trace element composition the first quartz generation is suggested to have been formed during eogenesis due to dissolution and replacement of feldspar the mesogenetic paragenesis comprises two generations of quartz and illite which are accompanied by albite in the solling sandstone sharp luminescence zoning in quartz overgrowths points to distinct episodes of cementation in both sandstones significant amounts of al li and h and traces of ge and b have been detected in the quartz overgrowths the al content of the quartz cements in the finefrau sandstones exceeds that in the quartz cements in the solling sandstone by a factor of five it is suggested that this compositional variation reflects the conditions in the pore water such as temperature and ph the al concentration is generally correlated to the li content with the exception of the latest quartz generation in the finefrau sandstones which is also most enriched in trace elements the ratio of li al varies between 0 11 and 0 25 in the two sandstones the li h ratio which ranges from 0 12 to 0 3 is controlled by the activity ratio of li and h in the pore fluid clay minerals are the most important source for li and high salinities favour the mobilization of li during diagenesis thus a relatively low salinity and low ph are responsible for the low li h ratio in the finefrau sandstone while high salinity and neutral to alkaline ph results in a high li h ratio for the solling sandstone the ge contents are generally near the average of detrital quartz and indicate that pressure dissolution is a major source for quartz cementation different chemical compositions of distinct quartz generations indicate changes in the physico chemical conditions and point to mobilization of silica from different sources for example pressure solution and clay mineral transformations

early quartz cements and evolution of paleohydraulic properties of basal sandstones in three paleoproterozoic continental basins evidence from in situ δ18o analysis of quartz cements quartz cement microstratigraphy and high precision in situ 18 o values obtained by secondary ion mass spectrometry sims from m size quartz cement zones have been used here to determine the timing of cementation and to evaluate precipitation mechanisms within the basal sandstones of three economically significant paleoproterozoic basins the athabasca and thelon basins canada and the mcarthur basin australia in these examples the earliest quartz cements have the highest 18 o values up to 33 mean 26 0 v smow indicative of low temperature precipitation at depths of 0 to 1 1 km some paragenetically early cement phases however have lighter isotopic values that suggest either precipitation from isotopically depleted water or precipitation at higher temperatures subsequent generations of quartz cements have progressively lower 18 o values mean 16 1 3 consistent with precipitation at higher temperatures these data combined with petrographic observations indicate quartz cementation began in near surface vadose and phreatic zones the next stage of cementation is characterized by syntaxial burial cement overgrowths regionally and stratigraphically well sorted sandstone facies that were initially aquifers preferentially experienced early quartz cementation which resulted in cement bridged pore throats at relatively shallow depths of 0 2 km and very early in their burial history transforming these units into diagenetic aquitards as a result these units did not experience mineralization compositionally and texturally immature braided fluvial facies did not experience early addition of quartz cement but are instead marked by minor syntaxial overgrowth cement that make upb5 of the intergranular volume formed at depths of 3 5 km and were variably replaced by illite and chlorite during burial these lithologies were still open to fluid movement at critical times in the basin when u and

fluid inclusions record thermal and fluid evolution in reservoir sandstones khatatba formation western desert egypt a case for fluid injection a fluid inclusion and petrographic study focused on quartz overgrowths was performed in reservoir sandstones from the jurassic khatatba formation salam oil field egypt s western desert the combination of detailed fluid inclusion petrography and scanning electron microscope sem cathodoluminescence imaging has allowed us to relate individual fluid inclusion assemblages that is the most finely discriminated groups of petrographically associated fluid inclusions to specific growth zones of authigenic quartz establishing the relative timing of entrapment of the inclusions after entrapment fluid inclusions in authigenic quartz have been preserved without reequilibration as indicated by the narrow ranges of homogenization temperatures 4 5 degreesc in most fluid inclusion assemblages three main growth zones are distinguished under sem cathodoluminescence in the quartz overgrowths and are termed q1 q2 and q3 from the oldest to the youngest zone q1 is further subdivided into three subzones and contains abundant primary aqueous inclusions their homogenization temperatures range from 162 to 130 degreesc with the earliest assemblages having the highest temperatures and with some large temperature fluctuations indicated between successive assemblages most q1 inclusions have salinities in the freshwater to seawater range with a trend toward increasing salinity through time zone q2 contains primary aqueous inclusions with homogenization temperatures overall range 148 125 degreesc also recording large temperature fluctuations and cooling events the q2 fluid inclusions have high salinities 5 20 wt nacl equivalent with salinity increasing through time zone q3 contains both aqueous and oil inclusions of primary origin the q3 aqueous inclusions have homogenization temperatures overall range 134 112 degreesc recording overall cooling and high salinities 21 24 wt nacl equivalent in early q3 subzones oil inclusions appear to be of medium gravity undersaturated with respect to gas in later q3 subzones oil inclusions are of gas saturated lighter oil our results indicate that fluid flow involving drastic changes in temperature and salinity was responsible for the precipitation of some of the quartz cement the earliest quartz q1 precipitated from freshwater and seawater at temperatures significantly higher than those expected from the burial history and thermal maturity of these rocks this quartz is interpreted to have precipitated during cooling of injected fluids that originated as hot connate fluids from deeper parts of the basin the q2 precipitation is interpreted to have resulted from episodes of injection of hot saline brines from below late quartz cement q3 precipitated during oil charge from progressively cooler and more saline brines interpreted to have refluxed from the surface it preserves a record of increasing oil maturity and gas saturation through time

tip to midpoint observations on syntectonic veins ouachita orogen arkansas trading space for time abstract by examining a vein from its tip to center we have established the transition from a single filled fracture at the vein tip to typical crack seal textures observed in fibered laminated veins the vein is contained in the boudin neck of a sandstone layer within the lower ordovician mazarn formation benton uplift ouachita orogen the tip of the vein is composed of one or more isolated veinlets defined as quartz filled narrow 5 25 m fractures parallel to the larger vein s long dimension scanned sem based cathodoluminescence shows that quartz laminae of the same orientation and thickness are found throughout the vein wall normal fibers first appear in the vein where detrital grains are cut by multiple veinlets each veinlet mimicking the crystallographic orientation of the detrital grain whereas later veinlets reflect the established crystallographic orientation of the fiber fibers throughout the vein retain evidence of having been formed by repeated fracturing and filling of a pre existing grain at the vein walls or fiber however recrystallization later modified the fibers by obliterating some evidence of the veinlets and moving fiber walls boudin formation provided the extension site that localized fracturing and vein filling the vein grows by the repeated addition of veinlets in the neck region recrystallization altered the shape of previously formed fibers

redox state during core formation on asteroid 4 vesta abstract core formation is the main differentiation event in the history of a planet however the chemical composition of planetary cores and the physicochemical conditions prevailing during core formation remain poorly understood the asteroid 4 vesta is the smallest extant planetary body known to have differentiated a metallic core howardite eucrite diogenite hed meteorites which are thought to sample 4 vesta provide us with an opportunity to study core formation in planetary embryos partitioning of elements between the core and mantle of a planet fractionates their isotopes according to formation conditions one such element silicon shows large isotopic fractionation between metal and silicate and its partitioning into a metallic core is only possible under very distinctive conditions of pressure oxygen fugacity and temperature therefore the silicon isotope system is a powerful tracer with which to study core formation in planetary bodies here we show through high precision measurement of si stable isotopes that hed meteorites are significantly enriched in the heavier isotopes compared to chondrites this is consistent with the core of 4 vesta containing at least 1 wt of si which in turn suggests that 4 vesta s differentiation occurred under more reducing conditions iw 4 than those previously suggested from analysis of the distribution of moderately siderophile elements in heds

destruction of a fluvial reservoir by hydrothermal activity cameros basin spain abstract this study provides an example of a high quality fluvial hydrocarbon reservoir that was completely destroyed by hydrothermal processes the reservoir unit was deposited in the cameros basin located in the nw sector of the iberian chain spain the basin was filled with clastic fluvial deposits sandstones and conglomerates between late berriasian and early aptian times provenance of sands was mainly from coarse crystalline rocks a humid tropical climate produced intense weathering of k feldspar during transport from source to basin thus a mineralogically mature rigid framework with high porosity existed at the time of deposition which would have constituted a high quality hydrocarbon reservoir at present however the porosity of the reservoir is negligible porosity was reduced by a sequence of diagenetic processes 1 mechanical compaction i e crushing of metamorphic lithic grains and chemical compaction 2 kaolinite and siderite cementation and 3 early quartz cementation hydrocarbon emplacement probably occurred between phases 2 and 3 a low grade metamorphic hydrothermal event reaching greenschist facies took place during the late cenomanian it dramatically reduced the remaining porosity of the reservoir and destroyed the hydrocarbon charge hydrothermal processes which affected the sandstones include 1 re compaction 2 late quartz cementation and silicification of remaining feldspars 3 carbonate cementation 4 chloritization of feldspars metamorphic lithic fragments and intrabasinal argillaceous grains and 5 growth of pyrite and chloritoid crystals on argillaceous material of intrabasinal extrabasinal or even diagenetic origin hydrocarbons that migrated to the margins of the basin escaped these hydrothermal modifications and were preserved the results of this study may be used to predict the diagenetic and hydrothermal evolution of other potential reservoirs in similar tectonic settings

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

diagenetic trends in the siliceous facies of the monterey shale in the santa maria region california x ray diffraction and oxygen isotopic analyses of outcrop and subsurface samples of siliceous rocks were used to reconstruct thermal and diagenetic histories of the miocene monterey shale near santa maria california within many stratigraphic sections soft porous diatomaceous rocks change gradationally to underlying hard and brittle chert porcellanite and siliceous shale the accompanying silica mineral zones are in descending stratigraphic order 1 biogenic silica opal a 2 cristobalitic silica opal ct and 3 microcrystalline quartz boundaries between silica mineral zones and stratigraphic horizons are often discordant within the opal ct zone the d 101 spacing of opal ct decreases in a smooth non linear fashion from about 4 10 a to 4 04 a in the santa maria valley and bradley oil field areas the thicknesses of the opal ct zones are greater and the present thermal gradients less than in the adjacent orcutt oil field thin opal ct zones at shallow maximum burial depths apparently correlate with higher thermal gradients using present thermal gradients and reconstructed maximum burial depths from well data in the santa maria region the ranges in temperatures for the top and base of the opal ct zone are 38 54 c and 55 110 c respectively the temperature difference between these two boundaries ranges from 17 to 60 c in comparison temperature ranges for these two boundaries computed from oxygen isotopic compositions of opal ct and quartz extrapolated experimental quartz water fractionations and assuming o18 0 o for the isotopic composition of the equilibrating fluid are 18 56 c and 31 80 c for the top and base of the opal ct zone respectively the temperature difference between these boundaries is 11 36 c using this method thermal gradients and sedimentation rates strongly influence rates of silica transformations reconstructed thermal and diagenetic histories of siliceous rocks of the monterey shale at four well sites in the santa maria region demonstrate that most silica conversions probably occurred during the last 3 4 myr in response to accelerated rates of sedimentation and therefore burial heating during the pliocene

quartz cementation history of sandstones revealed by high resolution sims oxygen isotope analysis abstract evaluating the timing and origin of quartz cement is central to understanding how porosity is lost in sandstones during burial kinetic models of quartz cementation have been calibrated using large scale datasets but have never been tested at the microscopic level at which cement forms here we use high precision in situ oxygen isotope analyses on sandstone from the jurassic ness formation from the north sea to reveal the growth history of single quartz overgrowths to a resolution of 2 m measured 18o cement range from 28 to 20 v smow in early to late cement and are consistent with quartz cementation models that propose the bulk of quartz precipitates as a continuous process beginning at 60 70 c quantitative x ray diffraction analyses and clay mineralogical analysis of interbedded shales are inconsistent with a silica source from shale implying that silica for the cement is sourced internally to the sand these isotope data are broadly consistent with predictive conceptual quartz cementation models and provide a critical link from micron scale measurements to basin scale predictions and observations

isotopic fractionation of zinc in tektites abstract tektites are terrestrial natural glasses produced during a hypervelocity impact of an extraterrestrial projectile onto the earth s surface the similarity between the chemical and isotopic compositions of tektites and terrestrial upper continental crust implies that the tektites formed by fusion of such target rock tektites are among the driest rocks on earth although volatilization at high temperature may have caused this extreme dryness the exact mechanism of the water loss and the behavior of other volatile species during tektite formation are still debated volatilization can fractionate isotopes therefore comparing the isotope composition of volatile elements in tektites with that of their source rocks may help to understand the physical conditions during tektite formation for this study we have measured the zn isotopic composition of 20 tektites from four different strewn fields almost all samples are enriched in heavy isotopes of zn compared to the upper continental crust on average the different groups of tektites are isotopically distinct listed from the isotopically lightest to the heaviest muong nong type indochinites 66 64 zn 0 61 0 30 north american bediasites 66 64 zn 1 61 0 49 ivory coast tektites 66 64 zn 1 66 0 18 the australasian tektites others than the muong nong type indochinites 66 64 zn 1 84 0 42 and central european moldavites 66 64 zn 2 04 0 19 these results are contrasted with a narrow range of 66 64 zn 0 0 7 for a diverse spectrum of upper continental crust materials the elemental abundance of zn is negatively correlated with 66 64 zn which may reflect that isotopic fractionation occurred by evaporation during the heating event upon tektite formation simple rayleigh distillation predicts isotopic fractionations much larger than what is actually observed therefore such a model cannot account for the observed zn isotope fractionation in tektites we have developed a more realistic model of evaporation of zn from a molten sphere during its hypervelocity trajectory the molten surface of the tektite will be entrained by viscous coupling with air that will then induce a velocity field inside the molten sphere this velocity field induces significant radial chemical mixing within the tektite that accelerates the evaporation process our model albeit parameter dependent shows that both the isotopic composition and the chemical abundances measured in tektites can be produced by evaporation in a diffusion limited regime

lithium isotopic composition of submarine basalts implications for the lithium cycle in the oceans abstract we have measured the li isotope composition of young pristine basalts from active ocean ridge crests of progressively older basalts along a dredging transect and a limited number of hydrothermally altered basalts the data significantly extend our limited knowledge of the isotopic abundance ratio of li in geological material fresh mid ocean ridge basalts have 6li values of between 3 4 and 4 7 relative to isotope standard l svec during low temperature weathering on the seafloor the isotopic composition of the rock becomes increasingly heavier due to addition of seawater li 6li 32 3 the oldest 46 m y and most altered rock studied has an isotopic composition of 14 a linear relationship exists between 6li and the inverse of li concentration suggesting that li in weathered basalts can be regarded as a two component mixture of basaltic li and seawater derived li that has been incorporated in alteration minerals most likely secondary clays such as smectite and phillipsite the inferred li isotopic composition of the alteration endmember indicates an apparent isotopic fractionation factor of 1 019 relative to the seawater source thus li uptake by secondary minerals from the low temperature weathering process and by analogy incorporation in similar authigenic minerals in marine sediments provides a mechanism for preferential removal of the lighter li isotope from ocean water however isotopic fractionation due to authigenic clay formation alone cannot account for the isotopic difference between seawater and its principal sources unless the hydrothermal flux is comparable to the river flux alternatively more important sinks of6li must exist if the steady state isotopic composition of li in ocean water is to be maintained

the lunar magma ocean reconciling the solidification process with lunar petrology and geochronology abstract the moon is thought to have originated with a magma ocean that produced a plagioclase flotation crust as solidification proceeded ages of anorthositic crust range over at least 200 million years the model for solidification presented here integrates chemical and physical constraints of lunar magma ocean solidification to determine 1 the final thickness of flotation crust generated by a fractionally solidifying magma ocean 2 the timescale of crystallization before plagioclase is a stable phase 3 the timescale of solidification after the formation of the plagioclase flotation crust and 4 the post overturn lunar mantle composition and structure we find that magma oceans of as much as 1000 km depth are consistent with creating an anorthositic crust 40 to 50 km in thickness solidification of the magma ocean prior to formation of the flotation crust may occur on the order of 1000 years and complete solidification would require additional ten to tens of millions of years reconciling these short model timescales with radiometric dates of crustal samples requires either a very late forming moon combined with finding older crustal ages to be incorrect or calling on tidal heating of the crust by the early earth to prolong solidification gravitationally driven overturn of cumulates during tidal heating provides a mechanism for creating the compositions and ages of the lunar mg suite of crustal rocks further we find that upon crystallization the moon likely began with an azimuthally heterogeneous gravitationally stable mantle after magma ocean cumulate overturn this result may help explain the experimentally determined origin of picritic glasses at similar depths but from different source materials

lithium isotope compositions of chondrules cai and a dark inclusion from allende and ordinary chondrites abstract bulk carbonaceous and ordinary chondrites have distinct li isotope compositions indicating the existence of local reservoirs and distinct formation conditions in the early solar system these differences may be also recorded in the components that compose chondrites here li concentrations and li isotope compositions of 89 chondrules 10 cai and 1 dark inclusion di from the allende cv3 meteorite and from 5 ordinary chondrites of low petrologic types semarkona bishunpur saratov bjurbole and bremervorde are presented in general chondrules have highly variable li isotope compositions ranging from 7li of 8 5 to 10 whereby the mean isotope composition of chondrules separated from a single chondrite is slightly lighter than its bulk remarkable however are the differences in li concentrations between bulk chondrite and chondrules of the entire set studied here 98 of the chondrules have significantly lower li abundances in the range of 0 2 to 0 75 g g than their hosts typically around 1 5 g g our results indicate that li elemental and isotopic fractionation has not occurred extensively during chondrule formation low but highly variable li abundances as well as the relatively large range in li isotopes point to small scale heterogeneities in the chondrule forming reservoir with respect to li such a non chondritic reservoir is unique to all chondrules the compositional differences in li isotopes between bulk carbonaceous and ordinary chondrites seitz et al 2007 are likely to be the result of mixing chondrules cai and matrix in different proportions

fingerprinting sources of orogenic plutonic rocks from variscan belt with lithium isotopes and possible link to subduction related origin of some a type granites lithium li elemental and isotope data are presented for a suite of plutonic rocks i s a and ss type coexisting mafic bodies from the western carpathians slovakia that were generated throughout the complete variscan orogenic cycle i type granites show a limited range of 7li contrasting with the large variations found in s type granites and orthogneisses of distinct ages this contradicts previous reports of predominantly light li s type granites sourcing metasedimentary lithologies and isotopically heavier i type granites derived from meta igneous sources an almost exclusively heavy li isotope signature 7li 4 7 found in four out of five a type granites rules out several commonly accepted petrogenetic scenarios such as remelting of granulitic residue after formation of i type granitic melts anatexis of calc alkaline meta igneous crust or extensive closed system fractional crystallization of mantle derived magmas instead it most probably reflects a derivation of a type granites from a mantle wedge modified by slab derived fluids during an early variscan or pan african subduction episode in contrast the distinct and lower 7li values 1 2 in the contemporaneous ss type granites can be related to their likely pelitic parentage mafic rocks gabbros and diorites associated with several occurrences of granites are uniformly li rich and isotopically light 0 5 precluding a direct derivation from the mantle these signatures testify to their cumulate origin whereby kinetic effects may be a viable explanation for the light li isotope compositions associated with diffusive redistribution of li between mantle derived mafic melts and acid magmas this corroborates recent studies on faster diffusion of 6li compared with 7li in natural systems taken together the presumed dichotomy between the sources and processes leading to generation of s and i type granitic magmas does not seem to be reflected by li isotope signatures in a simple and globally valid manner interpretation of li isotope compositions thus needs to be paralleled by other available information on petrology whole rock geochemistry and the magmatic context

mineralogical records of early planetary processes on the howardite eucrite diogenite parent body with reference to vesta abstract mineralogical information recovered from the howardite eucrite diogenite hed meteorites was employed to reconstruct the history of the parent body and relate it to 4 vesta these interpreted crustal evolution processes were then compared to the expected geological features on the surface of a likely proto planet 4 vesta the original crustal materials of the hed parent body were preserved as mineral grains and lithic clasts but in many eucrites fe mg ratios in pyroxenes were homogenized by diffusion after crystallization the crystallization trend of the protocrust has been deciphered by 1 examining monomict and crystalline samples and using their mineralogical and chemical information to formulate a sequence of crystallization and cooling trends and by 2 reconstructing the original crust prior to cratering events from lithic clasts and mineral fragments in polymict breccias such as howardites and polymict eucrites mineral components are identical both in the individual hed and in polymict breccias and no remnants of primitive materials were preserved in the polymict breccias a layered crust model reconstructed from such breccias consists of an upper crust with extrusive lava like eucrites that have been brecciated and metamorphosed diogenite mantle and cumulate eucrites of varying thickness between them this model can be used to explain the surface geological features of vesta observed from the hubble space telescope a large crater with diogenitic orthopyroxene at the crater floor is consistent with the deepest diogenitic layer of the layered crust model and an underlying olivine layer is expected from early crystallized olivine in the crystal fractionation model the old terrain of eucritic surface materials of vesta can be howardites polymict eucrites or regolith like eucrites produced from eucrites extruded and impacted on the surface partial melting models of eucrites seem to be favored by the rare earth element ree chemistry and experimental studies unfortunately partial melting models have not demonstrated how the hed parent body is converted to a layered crust without producing any metamorphosed primitive material in the layered crust the origin of cumulate eucrites with systematic variation of textures and chemistries of pyroxene can be explained by the layered crust model with excavation and mixing of trapped liquid discovery of basaltic materials with na rich plagioclase and augite in iron meteorites which are the products of partial melting suggests that eucrites may be unique to a body that underwent large scale differentiation and metamorphism

origin of quartz cements in some sandstones from the jurassic of the inner moray firth uk the extent of quartz cementation in shallow marine sandstones of the brora arenaceous formation oxfordian is closely related to the occurrence and abundance of rhaxella perforata sponge spicules three cement morphologies are identified chalcedonic quartz microquartz and mesoquartz chalcedonic quartz forms matrix supported cements which preserve moulds of rhaxella spicules chalcedonic quartz crystals have inequant development of crystal faces on average 0 1 m in diameter and are the first formed cement and reveal homogeneous dark grey tones on the sem cl bei microquartz forms 5 10 m diameter crystals which commonly grow on chalcedonic quartz substrates and show various grey tones under sem cl bei mesoquartz crystals grow in optical continuity with their host grains have 20 m a axial diameter crystals and exhibit distinctly zoned luminescence although no opaline silica is preserved the quartz cement is interpreted to have formed from an opaline precursor detrital quartz has an average 18o composition of 12 2 and mesoquartz syntaxial overgrowth has an average 18o composition of 20 0 estimates of the 18o compositions of microquartz and chalcedonic quartz are complicated by the problem of isolating the two textural types mixtures of the two give consistently higher 18o compositions than mesoquartz the higher estimate being 39 2 from oxygen isotope data the formation of quartz microquartz and chalcedonic quartz is interpreted to have taken place between 35 and 71 c in marine derived pore waters organic and inorganic maturation data constrain the upper temperature limit to less than 60 c

the origin of dark inclusions in allende new evidence from lithium isotopes aqueous and thermal processing of primordial materials occurred prior to and during planet formation in the early solar system a record of how solid materials were altered at this time is present in the carbonaceous chondrites which are naturally delivered fragments of primitive asteroids it has been proposed that some materials such as the clasts termed dark inclusions found in type iii chondrites suggest a sequence of aqueous and thermal events lithium isotopes 6li and 7li can reveal the role of liquid water in dark inclusion history during aqueous alteration 7li passes preferentially into solution leaving 6li behind in the solid phase and consequently any relatively extended periods of interaction with 7li rich fluids would have left the dark inclusions enriched in the heavier isotope when compared to the meteorite as a whole our analyses of lithium isotopes in allende and its dark inclusions reveal marked isotopic homogeneity and no evidence of greater levels of aqueous alteration in dark inclusion history

origin of quartz cement in the tirrawarra sandstone southern cooper basin south australia abstract quartz cement is the most abundant authigenic mineral in the fluvio deltaic tirrawarra sandstone and plays an important role in controlling reservoir quality quartz cement ranges from 0 to 19 and is controlled by the original sandstone composition petrographic fluid inclusion electron microprobe and cathodoluminescence cl data from the quartz cement indicate multiple stages of cementation at different temperatures and suggest more than one silica source cl observations indicate up to six stages of quartz cement in some samples the stages of quartz cement can be classified into three zones an innermost zone of brown luminescing cement z1 a middle zone of bright blue luminescing cement z2 and an outer zone of brown luminescing cement z3 dead oil or bitumen is trapped b tween z2 and z3 indicating that z3 formed after oil migration commenced measurements of homogenization temperatures from fluid inclusions in quartz overgrowths indicate that quartz cement precipitated over a temperature range of 65 to 130 c z1 quartz cement formed between 65 and 80 c and z2 cement was precipitated between 80 c and 100 c z3 quartz cement formed later at temperatures around 130 c microprobe analysis shows a consistent variation in aluminum between each quartz cement zone the average aluminum content for z1 z2 and z3 is respectively 237 538 and 58 ppm fluid inclusion precipitation temperatures and aluminum content have been used to help identify the silica sources for different zones of cement a likely source of silica for z1 quartz cement is early alteration of feldspar grains the bright blue cl color in the z2 quartz cement is related to its high aluminum content the source of silica for this cement is likely to have been late dissolution of feldspar grains by acidic fluids generated during kerogen maturation late quartz cement z3 has the lowest aluminum content which is similar to that of detrital quartz grains in the tirrawarra sandstone consi ering the temperature of precipitation very low aluminum content and the presence of z3 cement in facies prone to stylolitization the silica source for the cement is likely to have been pressure solution of detrital quartz at stylolites and grain contacts

fe mg fe mn relations of meteorites and primary heterogeneity of primitive achondrite parent bodies abstract we examine fe mg mn relations of meteorites as represented on plots of molar fe mg ratio vs molar fe mn ratio and use them to consider whether it is meaningful to classify achondrites as primitive or evolved first we demonstrate that fe mg fe mn plots can be used to identify some of the major processes that have affected meteorite parent bodies during both the nebular condensation and accretion and the planetary igneous stages of their evolution examination of compositions of chondrites on this diagram reveals distinct patterns that result from three nebular processes 1 volatility controlled mn mg fractionation 2 metal silicate fractionation under highly reducing conditions and 3 subsequent oxidation leading to variations in feo mgo ratio ordinary chondrites ocs show a characteristic pattern that records all three of these processes and suggests that the latter two are coupled examination of the compositions of achondrites on this diagram shows that all of those that have been classified as primitive lodranites acapulcoites winonaites iab silicate inclusions brachinites and ureilites are easily distinguished from those that have been classified as evolved sncs heds and lunar basalts the mn mg ratios of the former are chondritic while those of the latter are superchondritic hence they plot in two graphically distinct regions of the fe mg fe mn diagram a simple melting calculation reveals that this distinction results principally because the former are residues and the latter are melts or cumulate products of melts rather than because the latter are more evolved additionally however some of the groups classified as primitive achondrites show fe mg fe mn patterns similar to that of ocs constant but distinct mno mgo ratios over large ranges of feo mgo ratio we argue that these trends reflect primary heterogeneity resulting from the same nebular processes as those that affected ocs and therefore preserve evidence that more of the materials that accreted to form planetesimals experienced these processes than is apparent from known chondrites this evidence is preserved principally because these meteorites are residues in contrast groups commonly classified as evolved achondrites show fe mg fe mn patterns that reflect only igneous processing and any evidence for primary heterogeneity of their parent bodies has been obliterated again this is principally because these meteorites represent melts rather than beause they are more evolved usage of the terms primitive and evolved to describe achondrites should be clearly defined

recrystallization in quartz overgrowths quartz overgrowths are among the most volumetrically significant diagenetic phases in sandstones many combined petrographic and geochemical studies of quartz overgrowths rely heavily on the long held underlying assumption of their stability this study of sem cathodoluminescence sem cl imaging of quartz overgrowths from the jurassic khatatba formation of egypt calls this assumption into question these overgrowths preserve spectacular sem cl textures that can be interpreted as recrystallization fabrics there are three major growth zones in the overgrowths q1 to q3 in the first q1 fine sem cl zoning is preserved some with relict fibrous textures and smooth or bulging growth surfaces these textures could indicate initial precipitation as opaline silica chalcedony microquartz or some phase other than coarse quartz overgrowth in q1 there are discordant areas locally showing smooth and scalloped boundaries and filled with quartz with the sem cl character of later growth zones such textures suggest that earlier zones were crosscut by later phases of quartz the smooth and scalloped boundaries and their position in the overall framework of cements and grains are in places inconsistent with simple fracturing but are consistent with dissolution of earlier growth zones followed by filling with later quartz these features suggest that earlier growth zones were unstable and were replaced by coarsely crystalline quartz overgrowth such observations and other empirical and chemical considerations suggest that in some cases quartz overgrowths may result from recrystallization of less stable quartz and silica phases thus any study of sandstone diagenesis focused on quartz overgrowths should take this possibility into account

the effect of fluid chemistry on quartz microcrack lifetimes abstract metamorphic porosity consists of a branching hierarchy of primary features grain boundaries secondary features 3 and 4 grain junction tubules tertiary features microcracks and higher order features fractures while some of these features are rarely open to bulk fluid flow e g boundaries higher order features are open to fluid flow for timescales which vary significantly as a function of temperature pressure and fluid and rock chemistry the kinetics of microcrack healing in quartz between 300 600 c at 200 mpa increases as a function of fluid chemistry in the following order co 2 h 2 o 2 o m nacl 2 m cacl 2 6 m nacl changes in fluid chemistry which increase quartz solubility correlate with increased rates of healing these observations suggest that local redistribution of quartz occurs by solution precipitation driven by gradients in curvature along the crack surface and is possibly rate limited by pore fluid diffusion however the effect of crack geometry is larger than the effect of fluid chemistry at elevated temperatures and pressures aqueous fluids with elevated nacl concentrations can penetrate pervasively into polycrystalline quartz along a branching hierarchy consisting of episodically open fractures connected to 3 and 4 grain junction tubule networks while pure water or h 2 o co 2 fluid can only infiltrate pervasively along episodically open fractures 1 at lower temperatures and pressures 3 and 4 grain tubule networks in polycrystalline rocks may be closed to all fluids limiting fluid infiltration to microfacture networks lifetimes of quartz microcracks in all these fluids p fluid p confining is geologically short even at temperatures as low as 200 c

the meteoritical bulletin no 94 september 2008 the meteoritical bulletin 94 reports over 900 119 non antarctic and 803 antarctic newly approved meteorite names and their recovery histories macroscopic descriptions petrography mineral compositions and geochemistry meteorites reported include lunar martian howardites eucrites diogenites mesosiderites aubrites irons angrites ureilites acapulcoites lodranites and h l ll r co and cv chondrites eight of the meteorites in this bulletin are falls including 4 from india jodiya kaprada kavapura mahadevpur 1 from mali chergach turkey didim libya werdama and the u s berthoud

diagenesis of shallowly buried cratonic sandstones southwest sinai egypt abstract in spite of their age quartzose and feldspathic lower carboniferous sandstones deposited on the arabian shield in western sinai remain friable and porous average of 19 maximum of 25 except for strongly cemented ferricretes and silcretes these fluvial and shallow marine sandstones were not buried more than 1 5 km until late cretaceous and younger time when the deepest rocks reached 2 5 km owing to shallow burial depths and episodic exposure meteoric water dominated the pore system for most of geologic time iron oxides had multiple diagenetic stages and yield carboniferous and late cretaceous paleomagnetic signatures and oxygen isotopic data for authigenic quartz sparry calcite and kaolinite yield meteoric signatures the most significant diagenetic changes were 1 cementation by iron oxide that locally reaches 40 in groundwater ferricretes 2 reduction in porosity to 19 from an assumed original porosity 45 19 porosity was lost by compaction and 7 by cementation 3 generation of diagenetic quartzarenites by the loss of 7 detrital feldspar by kaolinization and dissolution and 4 development of three thin mature silcretes apparently by thermal groundwaters some outcrop samples have halite and gypsum cements of young but uncertain origin recycled from topographically higher younger rocks or from aerosols mature silcretes are strongly cemented by microcrystalline quartz multiply zoned syntaxial quartz and originally minor opal quartz overgrowths in most sandstones average only 2 2 but display a variety of textures and in places overprint isopachous opal now dissolved grain coats these features have more in common with incipient silcrete cement than normal burial quartz cement most silica was imported in groundwater

vesta as the howardite eucrite and diogenite parent body implications for the size of a core and for large scale differentiation if vesta is the parent body of the howardite eucrite and diogenite hed meteorites then geo chemical and petrologic constraints for the meteorites may be used in conjunction with astronomical constraints for the size and mass of vesta to 1 determine the size of a possible metal core in vesta and 2 model the igneous differentiation and internal structure of vesta the density of vesta and petrologic models for hed meteorites together suggest that the amount of metal in the parent body is 25 mass with a best estimate of 5 assuming no porosity for a porosity of up to 5 in the silicate fraction of the asteroid the permissible metal content is 30 these results suggest that any metal core in the hed parent body and vesta is not unusually large a variety of geochemical and other data for hed meteorites are consistent with the idea that they originated in a magma ocean it appears that diogenites formed by crystal accumulation in a magma ocean cumulate pile and that most noncumulate eucrites excepting such eucrites as bouvante and statinem formed by subsequent crystallization of the residual melts modelling results suggest that the hed parent body is enriched in rare earth elements by a factor of 2 5 3 5 relative to ci chondrites and that it has approximately chondritic mg si and al sc ratios stokes settling calculations for a vesta wide nonturbulent magma ocean suggest that early crystallizing magnesian olivine orthopyroxene and pigeonite would have settled relatively quickly permitting fractional crystallization to occur but that later crystallizing phases would have settled or floated an order of magnitude more slowly allowing instead a closer approach to equilibrium crystallization for the more evolved eucritic melts this would have inhibited the formation of a plagioclase flotation crust on vesta plausible models for the interior of vesta which are consistent with the data for hed meteorites and vesta include a metal core 130 km radius an olivine rich mantle 65 220 km thick a lower crustal unit 12 43 km thick composed of pyroxenite from which diogenites were derived and an upper crustal unit 23 42 km thick from which eucrites originated the present shape of vesta with 60 km difference in the maximum and minimum radius suggests that all of the crustal materials and possibly some of the underlying olivine from the mantle could have been locally excavated or exposed by impact cratering

geochemistry of cambro ordovician arbuckle limestone oklahoma implications for diagenetic δ18o alteration and secular δ13c and variation abstract isotopic analyses of 227 limestone samples from the cambro ordovician arbuckle group oklahoma document slow secular changes in the chemistry of the limestones from late cambrian to early ordovician the 18o values of the limestones increase from 10 to 7 pdb 13c values decrease from 0 to 2 pdb and 87 sr 86 sr ratios decrease from 0 7091 to 0 7088 the light 18o values suggest that all arbuckle limestones underwent diagenetic alteration probably caused by meteoric water recharged during the development of the overlying pre middle ordovician unconformity the gradual 18o increase from late cambrian to early ordovician reflects reduced 18o depletion with decreasing burial temperature during alteration although the presence of additional primary secular 18o variation cannot be ruled out the 13c and 87 sr 86 sr variations in accord with 13c and 87 sr 86 sr variations in the literature represent primary secular variations the variations indicate that the 13c value and 87 sr 86 sr ratio of early paleozoic surface seawater decreased from late cambrian to early ordovician the 13c variation during this time period seems to correlate with sea level variation specifically during sea level fall an increase in the rate of oxidation of organic matter caused 13c depletion of inorganic bicarbonate in seawater as a result early ordovician carbonates probably deposited during the regression stage of the latest precambrian to latest early ordovician cycle became 13c depleted relative to late cambrian carbonates the decrease of seawater 87 sr 86 sr ratio from late cambrian to early ordovician may have resulted from decreased riverine sr input caused by decreased rate of continental weathering

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

oxygen isotopic indications of the mechanisms of silica transport and quartz cementation in deeply buried sandstones the oxygen isotopic compositions and inferred precipitation temperatures of quartz cements in a suite of deeply buried sandstones from the north sea gulf coast and western canada basins indicate that in almost every case the quartz precipitated from 18 o rich basinal waters 18 o rich waters are found in strictly limited volumes in sedimentary basins silica transport and quartz cementation could not therefore have occurred as a result of large scale advection of basinal or meteoric waters because this would require very large fluid fluxes quartz cementation was driven by processes operating on a local scale the isotopic data do not uniquely indicate the mechanisms of silica transport but are consistent with both diffusion and local recycling of fluid

new evidence for the origin of quartz cements in hydrocarbon reservoirs revealed by oxygen isotope microanalyses quartz cements degrade hydrocarbon reservoir quality by choking off fluid flow paths therefore it is important to understand the sources and timing of quartz cementation we present in situ microanalyses of oxygen isotope ratios in quartz cements from a jurassic hydrocarbon reservoir located offshore norway showing systematic variations that reveal the isotopic history of the pore fluids that precipitated the quartz earliest quartz cements have 18o values of 20 26 subsequent cements drop in 18o value as low as 13 but then increase back to 23 with increasing cement thickness this isotopic trend was observed in multiple overgrowths with temperatures constrained by fluid inclusions and the burial history of the reservoir the isotopic composition of porewaters can be estimated from the measured isotopic ratios in quartz cement results indicate that 97 of the quartz cement precipitated from negative 18o waters originally meteoric that were gradually modified by burial diagenetic reactions as temperatures increased precipitation began in the middle to late cretaceous however the rate of quartz precipitation increased dramatically in the last 3 5 ma as the reservoir was rapidly buried the data show that quartz precipitation is a continuous process during burial and that silica is derived locally from silicate reactions occurring within the sandstone reservoir the isotopic data do not record evidence of episodic cementation from convection driven hot basinal fluids

secular boron isotope variations in the continental crust an ion microprobe study abstract tourmalines of various chemical compositions hosted in magmatic rocks with ages ranging from 3 8 ga to the present were analysed for 11 b by ion microprobe a large range of 11 b values from 2 to 30 1 5 was observed the 11 b values are correlated with the chemical composition of the tourmalines the li rich tourmalines being enriched in 11 b compared to fe and or mg rich tourmalines this may reflect mixing in the continental crust between a marine reservoir characterized by high li contents and 11 b values and a continental reservoir characterized by low li contents and 11 b values no relationship between the age and the 11 b values is observed for the fe or for the mg rich tourmalines in contrast the 11 b values of the li rich tourmalines show a tendency to regularly decrease with increasing age this pattern is consistent with a simple model of constant boron isotopic fractionation between seawater and the continental crust during the progressive extraction of the continents a variation in the mean 11 b value of the continental crust from 20 ga ago to 7 at present is predicted by the model the largest variation occurred during the first 2 5 ga

cathodoluminescent textures and the origin of quartz silt in oligocene mudrocks south texas abstract in subsurface mudrocks of the oligocene frio formation in south texas a substantial proportion of silt size quartz 10 62 m manifests cathodoluminescence cl that varies greatly in intensity within each particle giving rise to textures that differ greatly from grain to grain in contrast most quartz grains of sand size 62 m have cl that is relatively homogeneous within individual grains a substantial percentage of the quartz within silt grains is very weakly luminescent no depth trend in the occurrence of luminescent textures in detrital quartz is observed suggesting that the component of dark possibly low temperature silt size quartz is not related to chemical processes in the present burial setting paleogene rhyolites of west texas are a partial model for the source rocks that supplied sediment to the frio formation phenocrystic quartz in these volcanics has uniform cl similar to that observed in the frio sand fraction whereas complex cl structure seen in the associated groundmass bears many similarities to the cl textures observed in frio silts this observation further supports the idea that cl structure of detrital quartz in the frio is most likely an inherited feature if the quartz with dark cl is of low temperature origin it would help to elucidate the relatively 18o enriched isotopic values reported for mudrock quartz in the frio

ancient water on asteroid 4 vesta evidence from a quartz veinlet in the serra de mage eucrite meteorite abstract the meteorite serra de mage a eucrite inferred to be from the asteroid 4 vesta contains quartz veinlets they are identical to antitaxial or crack seal quartz veinlets in terrestrial rocks and are extraterrestrial and ancient because they pre date a 4 40 ga metamorphism the quartz was likely deposited from liquid water solutions as are terrestrial veins other potential solvents or transport mechanisms are inadequate or unlikely because there is no indication of internal magmatic water in the eucrite meteorites and thus in vesta the water from which the veinlet was deposited probably came from outside vesta by analogy with water ice deposits on the moon and mercury vesta and similar asteroids may have had or now have polar ice deposits possibly derived from comet impacts

water in lunar anorthosites and evidence for a wet early moon water has been detected on the lunar surface and attributed to delivery by impacts and the solar wind to a dry early moon spectroscopic detections of water in lunar anorthosites from the apollo collection suggest that a significant amount of water is indigenous to the moon

geochemistry of diogenites still more diversity in their parental melts we report on the major and trace element abundances of 18 diogenites and o isotopes for 3 of them our analyses extend significantly the diogenite compositional range both in respect of mg rich e g meteorite hills met 00425 mgo 31 5 wt and mg poor varieties e g dhofar 700 mgo 23 wt the wide ranges of siderophile and chalcophile element abundances are well explained by the presence of inhomogeneously distributed sulfide or metal grains within the analyzed chips the behavior of incompatible elements in diogenites is more complex as exemplified by the diversity of their ree patterns apart from a few diogenite samples that contain minute amounts of phosphate and whose incompatible element abundances are unlike the orthopyroxene ones the range of incompatible element abundances and particularly the range of dy yb ratios in diogenites is best explained by the diversity of their parental melts we estimate that the feo mgo ratios of the diogenite parental melts range from about 1 4 to 3 5 and therefore largely overlap the values obtained for non cumulate eucrites our results rule out the often accepted view that all the diogenites formed from parental melts more primitive than eucrites during the crystallization of a magma ocean instead they point to a more complex history and suggest that diogenites were derived from liquids produced by the remelting of cumulates formed from the magma ocean

timing of compaction and quartz cementation from integrated petrographic and burial history analyses lower cretaceous fall river formation wyoming and south dakota abstract integrated petrographic and burial history studies of fall river sandstones from outcrop and the subsurface provide insight into the timing of compaction and quartz cementation the two main porosity reducing processes in quartzose sandstones petrographic study of 95 thin sections of fall river fluvial valley fill sandstones from outcrop donkey creek field at 2 km burial depth and buck draw field at 3 8 km indicates that reservoir quality differs significantly in these three areas fall river sandstones at the surface contain an average of 31 intergranular volume igv and 2 quartz cement in both donkey creek and buck draw fields the sandstones average 22 igv but quartz cement volume averages 8 in the shallower field and 12 in the deeper geometric mean permeability at the urface is 4700 md compared with 42 md at 2 km and 2 md at 3 8 km burial history of the fall river sandstone differs greatly in the three areas the outcropping sandstones were buried to 2 km and had reached 80 c by the end of the cretaceous they were then uplifted and have remained at near surface temperatures since the paleocene the calculated time temperature index tti of these sandstones is 1 fall river sandstones at donkey creek were also buried to 2 km and had reached 80 c by the end of the cretaceous but remained at that depth during the tertiary tti is 14 in buck draw field fall river sandstones were buried to 2 5 km during the cretaceous and then continued to subside during the tertiary reaching depths of 4 km and temperatures of 140 c tti is 512 much of the compaction of fall river sandstones had occurred by burial depths of 2 km but additional time at that depth was required for completion of mechanical compaction and for minor chemical compaction although greater depth and higher temperatures did not increase chemical compaction increasing thermal maturity resulted in more quartz cementation internal sources of silica from stylolitization and intergranular pressure solution account for only 10 25 of the volume of quartz cement in fall river sandstones imported silica may have come from clay mineral transformations in cretaceous shales loss of porosity and permeability was greatest between tti of 1 and 14 but continued at a reduced rate as tti increased

amorphous silica nanofilms result in growth of misoriented microcrystalline quartz cement maintaining porosity in deeply buried sandstones deeply buried sandstones in sedimentary basins typically have low porosity due to cementation and compaction there are several known causes of anomalously high porosity in sandstones one of which is microquartz coatings on sand grains that seem to inhibit growth of quartz cement however there has been no mechanistic understanding of why or how microquartz grows or why it maintains high porosity in sandstones here we have used high resolution scanning electron microscopy electron backscattered diffraction and transmission electron microscopy to study the microquartz cemented late cretaceous heidelberg formation germany we have revealed that a nanofilm of amorphous silica 50 100 nm and a layer of chalcedony are between the detrital grain and microquartz cement the amorphous silica insulates the detrital quartz grains and prevents syntaxial growth while microquartz adopts the orientation of the underlying chalcedony with its fast growth c axis parallel to the grain surface thus preventing growth into the pore now that we know what controls microquartz growth and why it preserves porosity it can be used to help identify rank and appraise deeply buried petroleum accumulations

lithium in tektites and impact glasses implications for sources histories and large impacts abstract lithium li abundances and isotope compositions were determined in a representative suite of tektites moldavites muong nong type tektites and an australite ivory coast tektites and bediasites impact related glasses libyan desert glass zhamanshinites and irghizites a glass fragment embedded in the suevite from the ries impact crater and sedimentary materials in order to test a possible susceptibility of li to fractionation during hypervelocity impact events and to de convolve links to their potential parental sources the overall data show a large spread in li abundance 4 7 58 ppm li and 7 li values 3 2 to 26 0 but individual groups of tektites and impact glasses have distinctive li compositions most importantly any significant high temperature li isotope fractionation can be excluded by comparing sedimentary lithologies from central europe with moldavites instead we suggest that li isotope compositions in tektites and impact related glasses are probably diagnostic of the precursor materials and their pre impact geological histories the muong nong type tektites and australite specimen are identical in terms of li concentrations and 7 li and we tentatively endorse their common origin in a single impact event evidence for low temperature rayleigh fractionation which must have operated prior to impact induced melting and solidification is provided for a subset of muong nong type tektites although li isotope variations in most tektites are broadly similar to those of the upper continental crust libyan desert glass carries high 7 li 24 7 which appears to mirror the previous fluvial history of parental material that was perhaps deposited in lacustrine environment or coastal seawater lithium isotopes in impact related glasses from the zhamanshin crater define a group distinct from all other samples and point to melting of chemically less evolved mafic lithologies which is also consistent with their major and trace element patterns extreme shock pressures and the related extreme post shock temperatures alone appear not to have any effect on the li isotope systematics therefore useful information on parental lithologies and magmatic processes may be retrieved from analyses of martian and lunar meteorites moreover lack of significant li depletion in tektites provides further constraints on the loss of moderately volatile elements during the moon forming impact

volatilization induced by impacts recorded in zn isotope composition of ureilites ureilites are ultramafic achondrites formed by igneous processes early in the history of the solar system ureilites are heavily depleted in volatile elements probably by evaporation at the surface of the ureilite parent body however the moderately volatile element zn is an exception and its abundance is similar to cl volatilization can fractionate isotopes in a mass dependent manner therefore comparing the isotope composition of volatile elements in ureilites may better constrain the physical conditions during ureilite formation and the mechanism of origin of the variation of zn content for this study we measured the zn isotopic composition of 11 ureilites with a large range of zn content the elemental abundance of zn is negatively correlated with delta zn 66 which may reflect that isotopic fractionation occurred by evaporation during the heating event on the ureilite parent body simple rayleigh distillation predicts isotopic fractionations much larger than what is actually observed therefore such a model cannot account for the observed zn isotope fractionation in ureilites we propose that the observed isotopic fractionation can be produced by evaporation in a diffusion limited regime in addition the isotopic composition of zn is shown to be correlated with the shock grade of the ureilites this may indicate that the heating events responsible for the depletion in light isotopes in some ureilites were impacts c 2010 elsevier b v all rights reserved

sources of authigenic quartz in the permian tight sandstones close to gaoqing fault dongying sag bohai bay basin china abstract authigenic quartz is a significant cause of reduced porosity and permeability in the cement of the permian upper shihezi formation p2s sandstones in the gaoqing area dongying sag bohai bay basin china the sandstones are mainly quartzarenite with minor amounts of clay minerals authigenic quartz is generally the most commonly occurring cement and occurs as quartz overgrowth microfracture healing quartz pore filling quartz and microquartz in the sandstones three distinct separate phases of authigenic quartz i ii and iii were distinguished by using cathodoluminescence microscopy cl in the scanned cl images phase i quartz generally appears with light brown luminescence in the 450 670 nm range phase ii quartz is non luminescent in the 420 480 nm range and phase iii quartz appears with dark brown luminescence in the 470 650 nm range phase i quartz originating mainly from pressure solution has a composition similar to that of detrital quartz grains and was formed at approximately 79 3 104 c in the phase ii quartz li na mg2 al3 and ba2 are enriched and the homogenisation temperature of some aqueous inclusions is significantly higher than its maximum burial temperature of 130 c the eu of phase ii quartz is up to 1 42 the silica sources for phase ii quartz are dominated by hydrothermal fluids pressure solution feldspar dissolution and illitisation of smectite also provided a small amount of silica in the phase iii quartz all of the aqueous inclusions are almost higher than its maximum burial temperature al3 mg2 and rb are enriched in most of this quartz which was sourced mainly from hydrothermal fluids pressure solution also provided a very small amount of silica the hydrothermal fluids providing the silica source for phases ii and iii quartz migrated into the p2s sandstones along the adjacent gaoqing fault

lithium isotope geochemistry of the hawaiian plume results from the hawaii scientific drilling project and koolau volcano 1 we determined lithium isotopic compositions of mauna loa and mauna kea basalts from the 3 1 km drill hole of the hawaiian scientific drilling project hsdp for comparison li isotopic ratios were also determined for basalts from koolau volcano these two suites of samples define geochemical extremes in the range of hawaiian shield lavas the 400 ka record of mauna kea in the hsdp core shows temporal fluctuations between low 7li 4 relative to the l svec standard and high 7li 5 6 suggesting that the source components in the hawaiian plume are heterogeneous in li isotopic composition based on sio2 content and isotopic ratios of he li nd hf and pb three geochemical groups are identified in mauna kea lavas mauna kea basalts between 1900 and 2500 mbsl have relatively low 7li of about 4 they are low sio2 lavas distinguished by the highest 3he 4he and 208pb 204pb and low 176hf 177hf and 143nd 144nd like basalt from loihi seamount this mauna kea group is considered to originate from the core of the plume above 1900 mbsl high 7li lavas with high sio2 contents appear in both the submarine and subaerial sections they are marked by low 3he 4he and high 176hf 177hf the 7li rich signature of some samples 7li up to 5 7 is indicative of recycled oceanic crust in the plume this magma group defines the kea component the low sio2 lavas in the subaerial section have low 7li 4 3he 4he and 208pb 204pb their 7li values overlap the range of 7li in unaltered mid ocean ridge basalt morb and are consistent with upper mantle material entrained by the plume or contamination of plume derived magmas by the pacific lithosphere the 7li of koolau lavas mostly fall within the range of 4 5 0 3 exceptions are two samples that have 7li of 2 3 the lightest isotopic values may indicate subducted li that was isotopically fractionated during slab dehydration in contrast to other isotopic systems most koolau samples however resemble mauna kea samples in li isotopic composition mauna loa samples have 7li values of 3 5 to 4 9 within the range of the koolau and mauna kea lavas based on these data the loa trend volcanoes and kea trend volcanoes have largely overlapping li isotopic compositions in summary the hawaiian plume is not highly variable in li isotopic composition 7li is typically 4 with perturbations by subducted components to lower and higher ratios 2 5 to 5 7 the overlap of most hawaiian basalt and morb in their range of li isotopic ratios suggests minor influence of recycled oceanic crust in the plume and perhaps similar li isotopic ratios in the upper and lower mantle

spectroscopic characterization of mineralogy and its diversity across vesta the mineralogy of vesta based on data obtained by the dawn spacecraft s visible and infrared spectrometer is consistent with howardite eucrite diogenite meteorites there are considerable regional and local variations across the asteroid spectrally distinct regions include the south polar rheasilvia basin which displays a higher diogenitic component and equatorial regions which show a higher eucritic component the lithologic distribution indicates a deeper diogenitic crust exposed after excavation by the impact that formed rheasilvia and an upper eucritic crust evidence for mineralogical stratigraphic layering is observed on crater walls and in ejecta this is broadly consistent with magma ocean models but spectral variability highlights local variations which suggests that the crust can be a complex assemblage of eucritic basalts and pyroxene cumulates overall vesta mineralogy indicates a complex magmatic evolution that led to a differentiated crust and mantle

sr stable isotope composition of earth the moon mars vesta and meteorites abstract high precision stable sr isotopic variations 88 sr 86 sr are reported in a variety of terrestrial samples martian and lunar meteorites hed undifferentiated primitive meteorites chondrules and refractory inclusions almost all the whole rock samples are isotopically indistinguishable at a 50 parts per million ppm level the exceptions are cv and co chondrites which are isotopically light and for which we believe that their isotopic composition is controlled by the proportion of refractory material five separated chondrules and one refractory inclusion from allende are isotopically light with 88 86 sr fractionations up to 1 73 whereas the matrix is enriched in the heavy isotopes 88 86 sr 0 66 the depletion in heavy isotopes observed in chondrules and refractory inclusions could be attributed to the condensation of a material already depleted in sr however in that case more than 60 of the original material would be unaccounted we propose instead that isotopic fractionation by electromagnetic sorting of ionized heavy sr from neutral sr in the early solar system for the origin of the fractionation observed in refractory inclusions and redistribution of sr by aqueous alteration for the origin of the fractionation observed in chondrules and matrix we conclude that cv and co chondrites are not the primary building blocks for earth and mars

the effect of grain coating microquartz on preservation of reservoir porosity clay coatings have been widely accepted by many workers as an explanation for preserving high porosity in deeply buried sandstones but few workers have realized that similar effects can be produced by microcrystalline quartz coatings this phenomenon can be expected only under special circumstances but in such cases it can have profound consequences for exploration in the central graben area of the southern north sea unusually high porosity 20 27 and permeability 100 1000 md are found in certain zones in upper jurassic sandstones at depths of 3 4 4 4 km the porosity in these zones is 5 15 higher than expected based on average porosity depth trends from brent and haltenbanken sandstones we propose that the high porosity is due to continuous grain coatings of euhedral microcrystalline quartz crystals that are 0 1 2 m thick the distribution of microcrystalline quartz coatings is controlled by the presence of siliceous sponge spicules rhaxella which implies a sedimentological control on the reservoir quality we present a thermodynamic model showing how continuous microcrystalline quartz coatings inhibit development of no mal macrocrystalline quartz overgrowths sourced mainly from stylolites high porosities in parts of various upper jurassic oil fields ula and gyda have previously been explained by inhibition of quartz cementation by early hydrocarbon charge we suggest that the microcrystalline quartz coatings provide a more plausible explanation

elemental mapping by dawn reveals exogenic h in vesta s regolith using dawn s gamma ray and neutron detector we tested models of vesta s evolution based on studies of howardite eucrite and diogenite hed meteorites global fe o and fe si ratios are consistent with hed compositions neutron measurements confirm that a thick diogenitic lower crust is exposed in the rheasilvia basin which is consistent with global magmatic differentiation vesta s regolith contains substantial amounts of hydrogen the highest hydrogen concentrations coincide with older low albedo regions near the equator where water ice is unstable the young rheasilvia basin contains the lowest concentrations these observations are consistent with gradual accumulation of hydrogen by infall of carbonaceous chondrites observed as clasts in some howardites and subsequent removal or burial of this material by large impacts

isotopic composition of zinc copper and iron in lunar samples abstract we determined by icp ms the concentrations and isotopic ratios of fe cu and zn in the ti rich lunar basalt 74275 in the lunar orange glass 74220 and in up to 10 lunar soils namely 14163 15231 64501 66041 68841 69941 70011 72501 75081 and 76501 two analyses of zinc in lunar basalt 74275 give 66 zn 0 17 and 0 75 values within the range of those measured in terrestrial basalts copper in lunar basalt 74275 has 65 cu 1 4 which is isotopically heavier than values observed in terrestrial basalts in the orange glass we measured 56 fe 0 24 65 cu 0 42 and 66 zn 3 6 these values of are more negative than those obtained for 74275 and for typical lunar basalts but for cu comparable to those observed in terrestrial sulfides and meteorites in lunar soils we found 0 11 56 fe 0 51 2 6 65 cu 4 5 and 2 2 66 zn 6 4 insofar as we can generalize from a small sample set s fe cu zn and cd show similar trends in isotopic fractionation on the moon lunar basalts have nearly terrestrial isotopic ratios relative to the lunar basalt 74275 the pyroclastic glass 74220 is enriched in the lighter isotopes of fe cu and zn and the soils are enriched in the heavier isotopes of fe cu and zn the patterns in the basalts are likely inherited from the source material the light isotope enrichments seen in the orange glass originated during lava fountaining or less probably during partial condensation of vapor and the heavy isotope enrichments in the lunar soils were likely created by a combination of processes that included micrometeorite vaporization and sputtering in the orange glass the light isotope enrichments relative to lunar basalts of zn are larger than those of cu if these enrichments reflect accurately the isotopic composition of the gas they suggest that cu is more volatile than zn in the liquid from which the gas derived a simple model built on the known flux of micrometeorites to the lunar surface and a published estimate that micrometeorites generate 10 times their own mass of vapor predicts heavy isotope enrichments comparable to those observed in soils but only if the regolith gardening rate is set at about one twentieth of the generally accepted value of 1 cm my this discrepancy may reflect the difference in the time constants for micrometeorite milling and decimeter scale gardening or the importance of sputtering

iron and lithium isotope systematics of the hekla volcano iceland evidence for fe isotope fractionation during magma differentiation abstract in this study potential iron isotope fractionation by magmatic processes in the earth s crust was systematically investigated high precision iron isotope analyses by mc icp ms were performed on a suite of rock samples representative for the volcanic evolution of the hekla volcano iceland the whole series of hekla s rocks results from several processes i basaltic magmas rise and induce partial melting of meta basalts in the lower part of the icelandic crust the resulting dacitic magma evolves to rhyolitic composition through crystal fractionation during this differentiation the 56 54feirmm 014 values increase successively from 0 051 0 021 for the primitive dacites to 0 168 0 021 for the rhyolites this increase can be described by a rayleigh fractionation model using a constant bulk fractionation factor between all mineral phases m and the silicate liquid l of 56 54fem l 0 1 ii the basaltic magma itself differentiates by crystal fractionation to basaltic andesite composition no fe isotope fractionation was found in this series all basalts and basaltic andesites have an average 56 54feirmm 014 value of 0 062 0 042 2sd n 9 identical to mean terrestrial basaltic values reported in previous studies this observation is consistent with the limited removal of iron from the remaining silicate melt through crystal fractionation and small mineral melt fe isotope fractionation factors expected at temperatures in excess of 1050 c iii andesites are produced by mixing of basaltic andesite with dacitic melts the iron isotope composition of the andesites is matching that of the basaltic andesites and the less evolved dacites in agreement with a mixing process in the hekla volcanic suite li concentrations are positively correlated with indicators of magma differentiation all hekla rocks have 7li values typical for the upper mantle and demonstrate the absence of resolvable li isotope fractionation during crystal fractionation as a fluid mobile trace element li concentrations and isotopes are a potential tracer of magma fluid interaction at hekla li concentrations and isotope compositions do not indicate any extensive fluid exsolution hence the heavy fe isotope composition of the dacites and rhyolites can be predominately attributed to fractional crystallisation iron isotope analyses on single samples from other icelandic volcanoes torfajokull vestmannaeyjar confirm heavy fe isotope enrichment in evolving magmas our results suggest that the iron isotope composition of highly evolved crust can be slightly modified by magmatic processes

the bholghati howardite petrography and mineral chemistry abstract a 10 g sample of the bholghati howardite was disaggregated in order to separate two eucrite clasts several small carbonaceous clasts fragments of diogenitic pyroxene and bulk matrix the eucrite clasts show evidence of moderately rapid cooling from a melt followed by prolonged subsolidus annealing the carbonaceous clasts mostly resemble cm2 carbonaceous chondrites with low iron silicates and fe ni sulphides in a fine grained dark matrix one clast however is mineralogically petrographically and compositionally similar to a ci 1 chondrite both carbonaceous and eucritic clasts have a complex history prior to incorporation into the howardite matrix with no evidence of significant metamorphism since assembly most clasts in the howardite breccia are monomineralic with pyroxene and plagioclase pre dominant pyroxenes range from diogenitic to eucritic with diogenitic compositions most abundant a significant number of intermediate compositions are present consistent with derivation from a series of rocks related by fractionation

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

silicon isotopes in meteorites and planetary core formation the silicon si isotope compositions of 42 meteorite and terrestrial samples have been determined using mc icpms with the aim of resolving the current debate over their compositions and the implications for core formation no systematic 30si differences are resolved between chondrites 30si 0 49 0 15 2 sd and achondrites 30si 0 47 0 11 2 sd although enstatite chondrites are consistently lighter 30si 0 63 0 07 2 sd in comparison to other meteorite groups the data reported here for meteorites and terrestrial samples display an average difference 30sibse meteorite 0 15 0 10 which is consistent within uncertainty with previous studies no effect from sample heterogeneity preparation chemistry or mass spectrometry can be identified as responsible for the reported differences between current datasets the heavier composition of the bulk silicate earth is consistent with previous conclusions that si partitioned into the metal phase during metal silicate equilibration at the time of core formation fixing the temperature of core formation to the peridotite liquidus and using an appropriate metal silicate fractionation factor e 0 89 the 30sibse meteorite value from this study indicates that the earth core contains at least 2 5 and possibly up to 16 8 wt si

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

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

the crystallization age of eucrite zircon eucrites are a group of meteorites that represent the first planetary igneous activity following metal silicate differentiation on an early planetesimal similar to asteroid 4 vesta and thus help date geophysical processes occurring on such bodies in the early solar system using the short lived radionuclide 182hf as a relative chronometer we demonstrate that eucrite zircon crystallized quickly within 6 8 million years of metal silicate differentiation this implies that mantle differentiation on the eucrite parent body occurred during a period when internal heat from the decay of 26al and 60fe was still available later metamorphism of eucrites took place at least 8 9 million years after the zircons crystallized and was likely caused by heating from impacts or by burial under hot material excavated by impacts rather than from lava flows thus the timing of eucrite formation and of mantle differentiation is constrained