Vanadium isotopic composition and contents in gas-rich meteorites

We report ⁵⁰V/⁵¹V abundance ratio measurements and V concentrations for the dark portions of six gas-rich meteorites. These data and previous results for meteoritic, lunar and terrestrial samples indicate the same vanadium isotopic composition within the limits of error and, hence, place severe limits on possible differences in the irradiation histories of these materials. After application of necessary corrections, an average absolute abundance ratio of ⁵⁰V/⁵¹V= (2.425 ± 0.030) × 10^?3 is obtained.     

Nickel isotopic studies in meteorites

We have analyzed the nickel isotopic composition of meteoritic materials by high-precision mass spectrometry. The samples analyzed include almost all meteorite types for which large isotopic anomalies have been reported for oxygen, silver, magnesium and titanium. These samples are C₁, C₃, L, LL, H and E chondrites, IVB irons, Eagle Station pallasite and inclusion, matrix and “whole rock” samples of the Allende meteorite. The result is that we have not found any anomaly for nickel isotopic compositions within our accuracy of 0.7‰ for⁶¹Ni/⁶⁰Ni, 0.4-0.08‰ for⁶²Ni/⁶⁰Ni and 1–1.5‰ for⁶⁴Ni/⁶⁰Ni.     

Earth-like planets: one hot and rocky, one wet

Gravitational microlensing data combined with statistical analysis suggests that stars with solar systems like our own make up just 15% of the stars in our galaxy.     

Nitrogen abundances and isotopic compositions in stony meteorites

Nitrogen contents range from a few parts per million in ordinary chondrites and achondrites to several hundred parts per million in enstatite chondrites and carbonaceous chondrites. Four major isotopic groups are recognized: (1) C1 and C2 carbonaceous chondrites have δ¹⁵N of+30to+50%.; (2) enstatite chondrites have δ¹⁵N of?30to?40‰; (3) C3 chondrites have low δ¹⁵N with large internal variations; (4) ordinary chondrites have δ¹⁵N of?10to+20‰. The major variations are primary, representing isotopic abundances established at the time of condensation and accretion. Secondary processes, such as spallation reactions, solar wind implantation and metamorphic loss may cause small but observable isotopic variations in particular cases. The large isotopic difference between enstatite chondrites and carbonaceous chondrites cannot be accounted for by equilibrium condensation from a homogeneous nebular gas, and requires either unusually large kinetic effects, or a temporal or spatial variation of isotopic composition of the nebula. Nitrogen isotopic heterogeneity in the nebula due to nuclear processes has not been firmly established, but may be required to account for the large variations found within the Allende and Leoville meteorites. The unique carbonaceous chondrite, Renazzo, has δ¹⁵N of+170%., which is well beyond the range of all other data, and also requires a special source. It is not yet possible, from the meteoritic data, to establish the mode of accretion of nitrogen onto the primitive Earth.     

Ni isotopic compositions in Allende and other meteorites

A new technique for high-precision isotopic analyses of Ni was developed and applied to terrestrial samples, Allende inclusions and materials from other meteorites. Most of the Allende inclusions analysed here were previously reported to contain isotopically anomalous Ti. In contrast, the Ni isotopic abundances are indistinguishable from normal within presently obtainable precision with only one possible exception. The latter inclusion was shown by others to contain a significantly fractionated magnesium isotopic pattern of 9‰/amu. A normal Ni isotopic pattern has also been observed for the chromite/carbon fraction of an Allende acid residue which is known to contain heavy noble gases of highly anomalous isotopic composition. All other meteoritic samples analysed (Khohar matrix and chondrules, Murray matrix, a Tieschitz chondrule and an Orgueil magnetic fraction) also show normal isotopic compositions of Ni; no evidence for effects from now extinct⁶⁰Fe could be detected. In spite of ubiquitous isotopic anomalies in Ti from normal Allende inclusions, there is no signature of isotopic variations in Ni from the same samples. Possible constraints for the nucleosynthesis of iron peak elements and for astrophysical and cosmochemical conditions during formation of the solar system are discussed.     

Condensation and the composition of iron meteorites

The pressure-temperature conditions in the primordial nebula which could produce the observed Ni, Ga and Ge abundances in the major iron meteorite groups have been calculated assuming equilibrium condensation. Included in these calculations are the effect on the metal composition of Fe oxidation and sulphide formation during accretion, GeS and GaCl in the nebula gases and pressure variations in the nebula. It was found that the IIAB irons had their abundances of these elements fixed at the low-pressure extreme of the range which gives the IAB irons, but at 50 ± 10K higher temperatures. IIIAB and IVA formed over the same temperature range as IAB (600–670_?40⁺⁶⁰ K) in regions where the pressure was lower by a factor of 20 and 10⁴ respectively. Group IVB accreted soon after condensation of the metal and at pressures of less than 10^?3 atmosphere. The distribution of sulphur and carbon are consistent with this. The abundance of carbon in group IAB suggests that this and group IIAB accreted at about 10^?4 atmosphere, so that IIIAB and IVA accreted where the pressure was 5 × 10^?6 and 10^?8 atmosphere, respectively.     

Trace elements in shergottite meteorites: Implications for the origins of planets

The average concentrations of 19 siderophile and volatile elements in shergottite meteorites differ from those in terrestrial basalts by less than a factor of ten. This observation undermines claims that the abundances of siderophile and volatile elements in the Earth's upper mantle are uniquely terrestrial. Claims that similarities in the Moon's siderophile element pattern imply a terrestrial origin for the Moon are also weakened. The implication that basalt source regions on the asteroidal parent body of the shergottites resembled the terrestrial upper mantle constrains models of planetary formation and evolution. Heterogeneous accretion models may explain many of the similarities between these planets. Alternatively, separation of sulfide from basaltic magmas or their source regions on the Earth and the shergottite parent body may explain some of these similarities.     

Stable carbon and nitrogen isotopic composition of gas hydrate-bearing sediment from Hydrate Ridge,Cascadia Margin

Serious interest has been directed toward natural gas hydrate as a potential energy resource; factor in global climate change, and submarine geohazard since naturally occurring gas-hydrate deposits were found in the 1960s. Hydrate Ridge, Cascadia convergent mar- gin, is characterized by abundant methane hydrates at and below the seafloor, active venting of fluids and gases, chemosynthetic communities, and some of the highest methane oxidation rates ever found in the ma-rine environment. All of…     

The isotopic composition and elemental abundance of lutetium in meteorites and terrestrial samples and the 176Lu cosmochronometer

The isotopic composition of lutetium has been measured in a range of terrestrial and meteoritic materials using solid-source mass spectrometric techniques. The meteoritic and terrestrial isotopic abundances are identical within experimental errors. The absolute ¹⁷⁵Lu/¹⁷⁶Lu ratio as determined in this work is 37.36 ± 0.07 at the 95% confidence level. On the basis of this measurement the atomic weight of lutetium has been calculated to be 174.967 ± 0.002, which is in good agreement with the currently accepted figure of 174.97 ± 0.01.Using the stable isotope dilution technique the abundance of lutetium has been determined in 25 stone, 1 stony-iron and 8 iron meteorites, and in 12 standard rocks, with an accuracy of ±5% at the 95% confidence level. In general, there is good agreement between this work and other published data.The ¹⁷⁶Lu-¹⁷⁶Hf pair has been proposed as an s process nucleocosmochronometer, because of the long half-life of ¹⁷⁶Lu and the unique fact that both are s process isobars. The isotopic and elemental abundances of lutetium as measured in this work have been used with published nuclear data to estimate the mean age of s process nucleosynthesis for this isobaric pair, using the Schramm-Wasserburg formalism. The mean age cannot be accurately determined at the present time because of the lack of 30 keV neutron capture cross-section data for s only process nuclides and an accurate measurement of the branching ratio of ¹⁷⁵Lu + n. However, it is possible to place constraints on the nuclear parameters in this mass region using a reasonable s process chronology based on the decay of ¹⁷⁶Lu.     

Stable isotopic characterisation of francolite formation

Stable isotopic data are presented for 112 samples of francolite from 18 separate phosphate deposits. Values ofδ¹³C andδ³⁴S in most offshore deposits suggest formation within oxic or suboxic environments either by carbonate replacement or direct precipitation of francolite from water of normal marine compositions. The exceptions are concretionary francolite from Namibia, which has an isotopic composition in keeping with its formation within organic-rich sediments, and that from offshore Morocco, which has an isotopic signature of the anoxic/suboxic interface. Onshore deposits from Jordan, Mexico, South Africa and, possibly, the Permian Phosphoria Formation in the western U.S.A., are substantially depleted in¹⁸O: they appear to be too altered for deductions to be made about their environments of formation. In other onshore deposits which are unaltered, or minimally altered, the isotopic composition suggests that some formed within sulphate-reducing sediments (Sedhura, Morocco) whilst francolite from the Georgina Basin of Australia formed at the oxic/anoxic boundary, where oxidation of biogenic H₂S decreases theδ³⁴S of pore water. In general, pelletal samples show non-oxic isotopic signatures, whilst non-pelletal samples show oxic isotopic signatures, but samples from Namibia, Peru (Ica Plateau) and the Californian and Moroccan margins are exceptions to this rule. Morphology may therefore be a misleading indicator of francolite genesis as no definitive relation exists between phosphorite type and isotopic signature.     

Oxygen isotopic constraints on the origin of Mg-rich olivines from chondritic meteorites

Chondrules are the major high temperature components of chondritic meteorites which accreted a few millions years after the oldest solids of the solar system, the calcium–aluminum-rich inclusions, were condensed from the nebula gas. Chondrules formed during brief heating events by incomplete melting of solid dust precursors in the protoplanetary disk. Petrographic, compositional and isotopic arguments allowed the identification of metal-bearing Mg-rich olivine aggregates among the precursors of magnesian type I chondrules. Two very different settings can be considered for the formation of these Mg-rich olivines: either a nebular setting corresponding mostly to condensation–evaporation processes in the nebular gas or a planetary setting corresponding mostly to differentiation processes in a planetesimal. An ion microprobe survey of Mg-rich olivines of a set of type I chondrules and isolated olivines from unequilibrated ordinary chondrites and carbonaceous chondrites revealed the existence of several modes in the distribution of the ?¹⁷O values and the presence of a large range of mass fractionation (several ‰) within each mode. The chemistry and the oxygen isotopic compositions indicate that Mg-rich olivines are unlikely to be of nebular origin (i.e., solar nebula condensates) but are more likely debris of broken differentiated planetesimals (each of them being characterized by a given ?¹⁷O). Mg-rich olivines could have crystallized from magma ocean-like environments on partially molten planetesimals undergoing metal–silicate differentiation processes. Considering the very old age of chondrules, Mg-rich olivine grains or aggregates might be considered as millimeter-sized fragments from disrupted first-generation differentiated planetesimals. Finally, the finding of only a small number of discrete ?¹⁷O modes for Mg-rich olivines grains or aggregates in a given chondrite suggests that these shattered fragments have not been efficiently mixed in the disk and/or that chondrite formation occurred in the first vicinity of the breakup of these planetary bodies.     

Oxygen isotopic composition of low-temperature authigenic clinoptilolite

Oxygen isotope ratios were obtained from authigenic clinoptilolites from Barbados Accretionary Complex, Yamato Basin, and Exmouth Plateau sediments (ODP Sites 672, 797, and 762) in order to investigate the isotopic fractionation between clinoptilolite and pore water at early diagenetic stages and low temperatures. Dehydrated clinoptilolites display isotopic ratios for the zeolite framework (δ¹⁸O_f) that extend from +18.7‰ to +32.8‰ (vs. SMOW). In combination with associated pore water isotope data, the oxygen isotopic fractionation between clinoptilolite and pore fluids could be assessed in the temperature range from 25°C to 40°C. The resulting fractionation factors of 1.032 at 25°C and 1.027 at 40°C are in good agreement with the theoretically determined oxygen isotope fractionation between clinoptilolite and water. Calculations of isotopic temperatures illustrate that clinoptilolite formation occurred at relatively low temperatures of 17°C to 29°C in Barbados Ridge sediments and at 33°C to 62°C in the Yamato Basin. These data support a low-temperature origin of clinoptilolite and contradict the assumption that elevated temperatures are the main controlling factor for authigenic clinoptilolite formation. Increasing clinoptilolite δ¹⁸O_f values with depth indicate that clinoptilolites which are now in the deeper parts of the zeolite-bearing intervals had either formed at lower temperatures (17–20°C) or under closed system conditions.     

Chemical composition and rare gas content of four new detected antarctic meteorites

Within a region of 5 km × 10 km on a downhill slope of the Yamato Mounties, in 1969 the Japanese Expedition Team collected many stones. 9 of them were recognized as meteorites. On 4 of these findings we determined the chemical composition and the rare gas content. According to the mineralogical and the chemical composition, Yamato (a) is an enstatite chondrite, Yamato (b) a Ca-poor achondrite, Yamato (c) seems to be a carbonations chondrite Type III and Yamato (d) a olivine bronzite chondrite. Exposure ages are 1.7, 31, 25 and 4.3 my respectively.     

The osmium isotopic composition of organic-rich marine sediments

The osmium (Os) concentration and¹⁸⁷Os/¹⁸⁶Os ratio of several recent, marine, organic-rich sediment samples from three widely separated sites have been measured. Os concentrations range from 0.095 to 0.212 ppb and¹⁸⁷Os/¹⁸⁶Os ratios range from 8.2 to 8.9. The calculated fraction of hydrogenous Os exceeds 78% in all samples. Thus, the¹⁸⁷Os/¹⁸⁶Os ratio of these samples reflects Os isotopic composition of seawater. The small range in measured¹⁸⁷Os/¹⁸⁶Os ratio indicates that the Os isotopic composition at these sites is fairly homogeneous. The large magnitude of the Os burial flux at these sites indicates the Os burial in association with organic-rich sediments is an important sink in the marine cycle of Os. These data also suggest that ancient organic-rich sediments may provide a record of past variations in the Os isotopic composition of seawater.     

Stable isotopic analysis on ancient human bones in Jiahu site

Palaeodietary analysis is one of important topics in bioarchaeology field and has been paid great at- tention to by Chinese archaeometrists recently. Ancient human bones in Jiahu Site were analyzed by means of stable isotopes of C, N and O. 13 human bones were excluded from 28 bones for dietary re- construction due to their unusual collagen contents, C and N contents, and C/N atomic ratios espe- cially. δ 13C (-20.37±0.53‰) in collagen of remaining samples showed that C3 food were consumed mainly, which is consistent of the archaeological findings that rice was the staple in Jiahu. According to the difference of δ 15N and δ 13C values in bone collagen, the samples can be classified into four clusters. The changes of δ 15N values in bone collagen and δ 13C values in hydroxylapatite through whole cultural phases indicated the transition from hunting to gathering and fishing to rice agriculture and animal domestication ultimately. Meanwhile, the δ 18O change in hydroxylapatite showed that pa- laeoclimate was relatively constant during Jiahu culture.     

On the chemical composition of the Moon,Jupiter, meteorites and Am stars

If surface anomalies in the composition of the metallic-line A stars (Am stars) are due to a precipitation of planet-like bodies (planetoids) on them, then one should expect a correlation to exist between the overabundance of heavier-than-iron elements on these stars and their “standard” abundances in the solar system (since chondrites provide the “standard” level for these elements). However, an anticorrelation was revealed.Nevertheless, this fact supports the original suggestion on the origin of the metallicism of A stars, and can easily be explained within the author's hypothesis on the formation of the Sun from matter escaping from the proto-Jupiter. During the terminal stages of mass transfer, the matter was strongly depleted in refractories (forming the rocky core of Jupiter). Therefore the composition of the meteorites formed should not coincide with the primary composition of the matter. Thus the Sun's outer layers may also have a distorted composition. The author concludes that it is desirable to revise the “standard” abundances of elements heavier than iron.From a comparison of the surface composition of Am stars with the composition of lunar anorthosites and that of rocks in the upper zones of the Skaergaard intrusion (Greenland), the Am phenomenon may be seen to result from a precipitation of large geochemically differentiated planetoids onto a star. Such planetoids (including the Moon) condense in the cooled envelope of the primary component of a close binary stellar system.     

The isotopic composition of strontium in Central American ignimbrites

Voluminous sheets of rhyolitic ignimbrites were crupted during Miocene time in a region of Central America that is underlain by a thick sequence of middle Paleozoic and older metamorphic and plutonic rocks. Strontium isotopic ratios of fifteen ignimbrites range from 0.7035 to as high as 0.7175. These values are markedly higher than those measured for cale-alkaline lavas of the same province, but overlap the range found in basement rocks that may have served as source rocks for anateetic magmas. This relationship is in contrast to that found in the western United States where siliceous ignimbrites are not significantly richer in radiogenic strontium than are the basalt erupted through the same basement series. Several possible models for the origin of the large volumes of siliceous magma are examined in terms of major-element and isotopic relations, experimental studies of phase relations, and the thermal requirements of melting or assimilating basement rocks. A mathematical model for the effects of assimilation in open and closed systems permits a comparison of predicted chemical and isotopic compositions with those observed and places limits on the plausibility of various schemes of contamination with or without concurrent crystal fractionation. None of the models is without its flaws. Recent suggestions that large volumes of siliceous magma may be derived from the mantle or lower crust explain certain aspects of the Central American ignimbrites very well if one postulates that the high strontium ratios resulted from contamination of the magma with radiogenic strontium released by the break-down of mieas in basement rocks through which the magmas rose. Such a model fails to explain the apparent restriction of large rhyolitic ignimbrite cruptions to areas underlain by thick continental crust.     

Paleoclimate implication of oxygen and carbon isotopic composition from diagenesis coral

Oxygen and carbon isotopic compositions of diagenesis? coral samples from NY-1 core at the depth of 22 to 50 m, together with mineral compositions of transitive coral samples of 17 to 18 m at the depth, were meas ured. The data exhibited that when aragonite changed to calcite, its oxygen and carbon isotopic compositions dropped roughly on a linear trend. The linear trend implies that the oscillation pattern of the origin oxygen and carbon isotopic ratios of the aragonite could probably be retained after they diageneticly changed into calcite. Oxygen isotopic stratigraphy for the NY-1 core at the depth between 22 and 50 m was determined according to the δ⁸O ratios of the calcite coral. The oxygen stratigraphy provided an age of about 289 ka for 45 m of the NY-1 core, which agreed with that by paleomagnetic stratigraphy.     

The strontium isotopic composition of seawater,and seawater-oceanic crust interaction

The⁸⁷Sr/⁸⁶Sr ratio of seawater strontium (0.7091) is less than the⁸⁷Sr/⁸⁶Sr ratio of dissolved strontium delivered to the oceans by continental run-off (～0.716). Isotope exchange with strontium isotopically lighter oceanic crust during hydrothermal convection within spreading oceanic ridges can explain this observation. In quantitative terms, the current⁸⁷Sr/⁸⁶Sr ratio of seawater (0.7091) may be maintained by balancing the continental run-off flux of strontium (0.59 × 10¹² g/yr) against a hydrothermal recirculation flux of 3.6 × 10¹² g/yr, during which the⁸⁷Sr/⁸⁶Sr ratio of seawater drops by 0.0011. A concomitant mean increase in the⁸⁷Sr/⁸⁶Sr ratio of the upper 4.5 km of oceanic crust of 0.0010 (0.7029–0.7039) should be produced. This required⁸⁷Sr enrichment has been observed in hydrothermally metamorphosed ophiolitic rocks from the Troodos Massif, Cyprus.The post-Upper Cretaceous increase in the strontium isotopic composition of seawater(～0.7075–0.7091) covaries smoothly with inferred increase in land area. This suggests that during this period the main factor which has caused variability in the⁸⁷Sr/⁸⁶Sr ratio of seawater strontium could have been variation in the magnitude of the continental run-off flux caused by variation in land area. Variations in land area may themselves have been partly a consequence of variations in global mean sea-floor spreading rate.