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111.
Intercomparison of Boron Isotope and Concentration Measurements. Part II: Evaluation of Results 总被引:3,自引:1,他引:3
Roberto Gonfiantini Sonia Tonarini Manfred Grning Alessandra Adorni‐Braccesi Assad S. Al‐Ammar Marcus Astner Sebastien Bchler Ramon M. Barnes Randy L. Bassett Alain Cocherie Annette Deyhle Andrea Dini Giorgio Ferrara Jrme Gaillardet Judith Grimm Catherine Guerrot Urs Krhenbühl Graham Layne Damien Lemarchand Anette Meixner D. Jack Northington Maddalena Pennisi Eva Reitznerov Ilia Rodushkin Naoji Sugiura Regina Surberg Sabine Tonn Michael Wiedenbeck Samuel Wunderli Yingkai Xiao Thomas Zack 《Geostandards and Geoanalytical Research》2003,27(1):41-57
The Istituto di Geoscienze e Georisorse (IGG), on behalf and with the support of the International Atomic Energy Agency (IAEA), prepared eight geological materials (three natural waters and five rocks and minerals), intended for a blind interlaboratory comparison of measurements of boron isotopic composition and concentration. The materials were distributed to twenty seven laboratories - virtually all those performing geochemical boron isotope analyses in the world -which agreed to participate in the intercomparison exercise. Only fifteen laboratories, however, ultimately submitted the isotopic and/or concentration results they obtained on the intercomparison materials. The results demonstrate that interlaboratory reproducibility is not well reflected by the precision values reported by the individual laboratories and this observation holds true for both boron concentration and isotopic composition. The reasons for the discrepancies include fractionations due to the chemical matrix of materials, relative shift of the zero position on the δ11 B scale and a lack of well characterized materials for calibrating absolute boron content measurements. The intercomparison materials are now available at the IAEA (solid materials) and IGG (waters) for future distribution. 相似文献
112.
Volcanic arcs of the Southwest Pacific, collectively referred to as the Outer Melanesian Arc, are generally thought to result from subduction of the Pacific Plate since the Late Cretaceous. Meanwhile, it is largely accepted that eastward roll-back of the old and dense oceanic plate allowed opening of marginal basins, which isolated large blocks of the former Gondwana margin. Incidentally, some ‘intra-oceanic’ volcanic arcs may have been nucleated on small continental fragments. Detrital zircons collected from sand banks in the mid-reaches of rivers from Viti Levu Island have been analysed for U–Pb geochronology and geochemistry, in order to search for a possible ancient continental arc basement, remnants of a Late Cretaceous arc, and determine the timing and evolution of Fiji arc magmatism. In contrast with some other places of the Outer Melanesian Arc (Solomon, Vanuatu), no pre-upper Eocene zircons have been found. Thus, Gondwana-derived fragments or Late Cretaceous–Paleocene arc remnants are unlikely to form the basement of Viti Levu. Zircon geochemistry confirms the purely intra-oceanic character of volcanic-arc magmatism as well. Variations in some trace-element ratios closely reflect the evolution of Viti Levu Arc from upper Eocene inception to upper Miocene climax and finally Pliocene intra-arc rifting and abandonment. 相似文献
113.
Dario Dello Iacono Aldo Zollo Maurizio Vassallo Tiziana Vanorio Sebastien Judenherc 《Bulletin of Volcanology》2009,71(3):275-284
In September 2001, an extensive active-seismic investigation (Serapis experiment) was carried out in the Gulfs of Naples and
Pozzuoli, with the aim of investigating and reconstructing the shallow crustal structure of the Campi Flegrei caldera, and
possibly identifying its feeding system at depth. The present study provides a joint analysis of the very shallow seismic
reflection data and tomographic images based on the Serapis dataset. This is achieved by reflection seismic sections obtained
by the 3D data gathering and through refined P-velocity images of the shallowest layer of Pozzuoli Gulf (z < 1,000 m). From the refined Vp model, the overall picture of the velocity distribution confirms the presence of a complex
arc-shaped anomaly that borders the bay offshore. The deeper part of the anomaly (beneath 700 m, with Vp > 3,500 m/s) correlates
with units made up of agglomerate tuffs and interbedded lava, which form the southern edge of the caldera, which was probably
formed following the two large ignimbritic eruptions that marked the evolutionary history of the area under study. The upper
part of the anomaly that tends to split into two parallel arcs is correlated with dikes, volcanic mounds and hydrothermal
alteration zones noted in previous shallow reflection seismic analyses. The depth of the transition between the upper and
lower parts of the anomaly is characterized by an abrupt Vp increase on the one-dimensional (1D) profiles extracted from the
3D tomographic model and by the presence of a strong reflector located at about 0.6/0.7 s Two Way Time (TWT) on Common Mid
Point gathers. The move-out velocity analysis and stack of the P–P and P–S reflections at the layer bottom allowed to estimate
relatively high Vp/Vs values (3.7 ± 0.9). This hypothesis has been tested by a theoretical rock physical modeling of the Vp/Vs
ratio as a function of porosity suggesting that the shallow layer is likely formed by incoherent, water saturated, volcanic
and marine sediments that filled Pozzuoli Bay during the post-caldera activity. 相似文献
114.
A note on 10Be‐derived mean erosion rates in catchments with heterogeneous lithology: examples from the western Central Andes 下载免费PDF全文
Sebastien Carretier Vincent Regard Riccardo Vassallo Joseph Martinod Frederic Christophoul Eric Gayer Laurence Audin Christelle Lagane 《地球表面变化过程与地形》2015,40(13):1719-1729
Millennial catchment–mean erosion rates derived from terrestrial cosmogenic nuclides are generally based on the assumption that the lithologies of the parent rock each contain the same proportion of quartz. This is not always true for large catchments, in particular at the edge of mountainous plateaus where quartz‐rich basement rocks may adjoin sedimentary or volcano‐sedimentary rocks with low quartz content. The western Central Andes is an example of this type of situation. Different quartz contents may be taken into account by weighting the TCN production rates in the catchment. We recall the underlying theory and show that weighting the TCN production rate may also lead to bias in the case of a spatial correlation between erosion rate and lithology. We illustrate the difference between weighted and unweighted erosion rates for seven catchments (16 samples) in southern Peru and northern Chile and show variations up to a factor of 2 between both approaches. In this dataset, calculated erosion rates considering only granitoid outcrops are better correlated with catchment mean slopes than those obtained without taking into account the geological heterogeneity of the drained watershed. This dataset analysis demonstrates that weighting erosion rates by relative proportions of quartz is necessary to evaluate the uncertainties for calculated catchment–mean erosion rates and may reveal the correlation with geomorphic parameters. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
115.
Sebastien Leblond Sandrine Gombert Jean Louis Colin Remi Losno Catherine Rausch De Traubenberg 《Journal of Atmospheric Chemistry》2004,49(1-3):95-110
Over a period of one year, the moss Scleropodium purum was sampled every two weeks in a French rural area to determine the levels of Li, Na, Al, Si, P, Ca, V, Mn, Fe, Zn, Ba, Hg, and Pb. The element distribution in the moss shoot was studied throughout the year. An apical bioconcentration was discovered for Na, P, Ca, Mn, and Zn, whereas higher levels were found in the basal fraction for Li, Al, Si, V, Fe, Ba, Hg, and Pb. A significant variation of element concentrations was observed during the sampling period. In the apical part Li, Al, Si, V, Fe, Ba, and Hg show maximum levels in the summer and minimum in the autumn. The same pattern was found with Ca and Mn in the whole plant, whereas Na showed opposite fluctuations. 相似文献
116.
Computer simulation of electron transfer at hematite surfaces 总被引:1,自引:0,他引:1
Molecular dynamics simulations in combination with ab initio calculations were carried out to determine the rate of electron transfer at room temperature in bulk hematite (α-Fe2O3) and at two low-index surfaces, namely the (012) and (001) surfaces. The electron transfer reactions considered here involve the II/III valence interchange between nearest-neighbor iron atoms. Two electron transfer directions were investigated, namely the basal plane and c direction electron transfers. Electron transfer rates obtained in bulk hematite were in good agreement with ab initio electronic structure calculations thus validating the potential model. The surfaces were considered both in vacuum and in contact with an equilibrated aqueous solution. The reorganization energy is found to increase significantly at the first surface layer and this value is little affected by the presence of water. In addition, in the case of the (012) surface, the electronic coupling matrix element for the topmost basal plane transfer was calculated at the Hartree-Fock level and was found to be weak compared to the corresponding electron transfer in the bulk. Therefore, most surfaces show a decrease in the rate of electron transfer at the surface. However, where iron atoms involved in the electron transfer reaction are directly coordinated to water molecules, water lowers the free energy of activation to a great extent and provides a large driving force for electrons to diffuse toward the bulk thus opposing the intrinsic surface effect. The surfaces considered in this work show different electron transfer properties. Hematite has been shown to exhibit anisotropic conductivity and thus different surfaces will show different intra- and inter-layer rates depending on their orientation. Moreover, the calculations of electron transfers at the hydroxyl- and iron-terminated (001) surfaces revealed that surface termination has a significant effect on the electron transfer parameters in the vicinity of the surface. Finally, our findings indicate that undercoordinated terminal iron atoms could act as electron traps at the surface. 相似文献
117.
The key role of mica during igneous concentration of tantalum 总被引:2,自引:0,他引:2
Aleksandr Stepanov John A. Mavrogenes Sebastien Meffre Paul Davidson 《Contributions to Mineralogy and Petrology》2014,167(6):1-8
Igneous rocks with high Ta concentrations share a number of similarities such as high Ta/Nb, low Ti, LREE and Zr concentrations and granitic compositions. These features can be traced through fractionated granitic series. Formation of Ta-rich melts begins with anatexis in the presence of residual biotite, followed by magmatic crystallization of biotite and muscovite. Crystallization of biotite and muscovite increases Ta/Nb and reduces the Ti content of the melt. Titanium-bearing oxides such as rutile and titanite are enriched in Ta and have the potential to deplete Ta at early stages of fractionation. However, mica crystallization suppresses their saturation and allows Ta to increase in the melt. Saturation with respect to Ta and Nb minerals occurs at the latest stages of magmatic crystallization, and columbite can originate from recrystallization of mica. We propose a model for prediction of intrusion fertility for Ta. 相似文献
118.
Rubies and sapphires are of both scientific and commercial interest. These gemstones are corundum colored by transition elements within the alumina crystal lattice: Cr3+ yields red in ruby and Fe2+, Fe3+, and Ti4+ ionic interactions color sapphires. A minor ion, V3+ induces slate to purple colors and color change in some sapphires, but its role in coloring rubies remains enigmatic. Trace element and oxygen isotope composition provide genetic signatures for natural corundum and assist geographic typing. Here, we show that V can dominate chromophore contents in Mogok ruby suites. This raises implications for their color quality, enhancement treatments, geographic origin, exploration and exploitation and their comparison with rubies elsewhere. Precise LA-ICP-MS analysis of ruby and sapphire from Mogok placer and in situ deposits reveal that V can exceed 5,000 ppm, giving V/Cr, V/Fe and V/Ti ratios up to 26, 78, and 97 respectively. Such values significantly exceed those found elsewhere suggesting a localized geological control on V-rich ruby distribution. Our results demonstrate that detailed geochemical studies of ruby suites reveal that V is a potential ruby tracer, encourage comparisons of V/Cr-variation between ruby suites and widen the scope for geographic typing and genesis of ruby. This will allow more precise comparison of Asian and other ruby fields and assist confirmation of Mogok sources for rubies in historical and contemporary gems and jewelry. 相似文献
119.
Sebastien Bouquain N. T. Arndt E. Hellebrand F. Faure 《Contributions to Mineralogy and Petrology》2009,158(5):599-617
We present a detailed mineralogical and major- and trace-element study of pyroxenes in two Archean komatiitic flows in Alexo,
Canada. The pyroxenes in spinifex-textured lavas commonly are zoned with cores of magnesian pigeonite and rims of augite.
Concentrations of incompatible trace elements are low in pigeonite and jump to higher values in the augite mantles, a variation
that can be modelled using accepted partition coefficients and assuming crystallization from komatiitic liquids. Crystallization
sequences are very different in different parts of both flows. In the flow top, the sequence is olivine followed by augite:
deeper in the spinifex sequence, pigeonite crystallizes after olivine, followed by augite; in lower cumulates, orthopyroxene
or augite accompany olivine. In spinifex lavas, pigeonite crystallizes sooner than would be predicted on the basis of equilibrium
phase relations. We propose that contrasting crystallization sequences depend on the position in the flow and on the conditions
of crystal growth. In the flowtop, rapid cooling causes quench crystallization. Deeper in the spinifex layer, constrained
growth in a thermal gradient, perhaps augmented by Soret differentiation, accounts for the early crystallization of pigeonite.
The cumulus minerals represent a near-equilibrium assemblage. Augites in Al-undepleted Archean komatiites in various localities
in Canada and Zimbabwe have high moderate to high Wo contents but their Mg# (Mg/(Mg + Fe) are lower than in augites in komatiites
from Barberton, South Africa. We attribute the combination of high Wo and high Mg# in Barberton rocks to the unusually high
CaO/Al2O3 of these Al-depleted komatiites. 相似文献