Abundance of 17 trace elements in carbonaceous chondrites     

Urs Krähenbühl  John W. Morgan  R. Ganapathy  Edward Anders 《Geochimica et cosmochimica acta》1973,37(5):1353-1370

Seventeen trace elements (Ag, Au, Bi, Br, Cd, Cs, Ge, In, Ir, Rb, Re, Sb, Se, Te, Tl, U and Zn) were measured by neutron activation analysis in 8 C1 samples (1 Alais, 3 Ivuna, 4 Orgueil) and in 3 C2 samples (one each of Mighei, Murchison, Murray). The results show far less scatter than earlier literature data. The standard deviation of a single measurement from the mean of 8 C1 samples lies between 2 and 14 per cent, except for the following 4 elements: Au ±18 per cent, Ag ±22 per cent, Rb ±19 per cent and Br ±33 per cent. The first two probably reflect contamination and sample heterogeneity, the last two, analytical error. Apparently C1 chondrites have a far more uniform composition than some authors have claimed.The new data suggest significant revisions in cosmic abundance for the following elements (old values in parentheses): Zn 1250 (1500), Cd 1.51 (2.12), Ir 0.72 (0.43) atoms/10⁶ Si atoms. The Br value is also lower, 6.8 vs 20.6, but may be affected by analytical error.Relative to C1 chondrites, the C2 chondrites Mighei, Murchison and Murray are depleted in volatile elements by a factor of 0.508 ± 0.038, much more constant than indicated by oldor data. Ordinary chondrites also show a more uniform depletion relative to the new C1 data. The mean depletion factor of Sb, F, Cu, Ga, Ge, Sn, S, Se, Te and Ag is 0.227 ± 0.027 in H-chondrites. This constancy further strengthens the case for the two-component model of chondrite formation.  相似文献   

Longitudinal effects of experimental floods on stream benthos downstream from a large dam     

Christian?Jakob  Christopher?T.?RobinsonEmail author  Urs?Uehlinger 《Aquatic Sciences - Research Across Boundaries》2003,65(3):223-231

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Microstructure of 24-1928 Ma concordant monazites; implications for geochronology and nuclear waste deposits   总被引：1，自引：0，他引：1  

Anne-Magali Seydoux-Guillaume  Richard Wirth  Urs Schärer 《Geochimica et cosmochimica acta》2004,68(11):2517-2527

The microstructure of monazite was studied using scanning electron microscopy (SEM), electron microprobe analysis (EMP), X-ray diffraction patterns (XRD), and transmission electron microscopy (TEM). Four well-characterized monazites were investigated, having very different concordant U-Pb ages (24 to 1928 Ma), and up to ∼15 wt.% ThO₂, and ∼0.94 wt. % UO₂. The SEM and EMP analyses of polished single crystal fragments reveal the absence of significant chemical zoning. XRD and TEM investigations show that the monazites are not metamict, despite their old ages, very high abundances of radionuclides, and hence, high time-integrated radiation doses. Except for the youngest one, the monazite crystals are composed of a mosaic of crystalline but slightly distorted domains. This structure is responsible for the presence of (1) mottled diffraction contrasts on the TEM, and (2) a second structural phase (B), with very broad reflections in the XRD patterns. Older monazites receive higher self-irradiation doses, and hence, they contain higher amounts of this B-phase. For the 1928 Ma monazite, XRD reveals only the broad reflections of phase B, implying that the whole monazite was affected by radiation damage that resulted in total distortion of the lattice. It is concluded that radiation damage in the form of amorphous domains does not accumulate in monazite because self-annealing heals the defects as they are produced by α-decay damage. The only memory of irradiation-induced defects is the presence of distorted domains. As the diffusion rate of Pb in an undisturbed monazite lattice is extremely low, Pb loss due to volume diffusion out of the monazite lattice is virtually impossible. This is considered as one reason why almost all monazites have concordant U-Th-Pb ages. Moreover, as long-term self-irradiation effects are limited in monazite, we consider this phase as a good candidate for the storage of high-level nuclear waste under the aspect of its high resistance to irradiation.  相似文献   

Understanding the pre-Variscan and Variscan basement components of the central Tauern Window, Eastern Alps (Austria): constraints from single zircon U-Pb geochronology     

Tesfaye Kebede  Urs Klötzli  Jan Kosler  Torbjörn Skiöld 《International Journal of Earth Sciences》2005,94(3):336-353

New single-grain and within-grain U-Pb zircon ages from the central Tauern Window help sorting out the time dimension among the various Variscan and pre-Variscan basement components that were strongly overprinted by Alpine orogeny. Single-grain isotope dilution (ID-TIMS) U-Pb zircon geochronology of three Basisamphibolit samples yield protolith formation ages of 351±2, 349±1 and 343±1 Ma. Laser ablation ICP-MS and ID-TIMS U-Pb detrital zircon dating of the Biotitporphyroblastenschiefer constrained the maximum time of sedimentation to between 362±6 Ma and 368±17 Ma. Paragneisses from the Zwölferzug yield maximum sedimentation ages from 345±5 Ma (ion microprobe data) to 358±10 Ma. Zircons from gabbroic clasts and detrital zircons from a meta-agglomerate from the Habach Phyllite give an upper intercept age of 536±8 Ma and a near-concordant age of 506±9 Ma, respectively. Hence, apart from the Habach Phyllite, the maximum sedimentation ages of the metasediments investigated range from Upper Devonian to Lower Carboniferous. Consequently, the Basisamphibolit, the Biotitporphyroblastenschiefer, and the paragneisses of the Zwölferzug form parts of the Variscan basement series. The Basisamphibolit (351-343 Ma) is distinct both in space and time of formation from the Zwölferzug garnet amphibolite (c. 486 Ma), which forms part of the pre-Variscan basement.  相似文献   

Earthquakes in Switzerland and surrounding regions during 2005     

Nicolas Deichmann  Manfred Baer  Jochen Braunmiller  Stephan Husen  Donat F?h  Domenico Giardini  Philipp K?stli  Urs Kradolfer  Stefan Wiemer 《Eclogae Geologicae Helvetiae》2006,99(3):443-452

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The Greenland Ice Core Chronology 2005, 15–42 ka. Part 1: constructing the time scale     

Katrine K. Andersen  Anders Svensson  Sigfus J. Johnsen  Sune O. Rasmussen  Matthias Bigler  Regine Rthlisberger  Urs Ruth  Marie-Louise Siggaard-Andersen  Jrgen Peder Steffensen  Dorthe Dahl-Jensen  Bo M. Vinther  Henrik B. Clausen 《Quaternary Science Reviews》2006,25(23-24):3246

The Greenland Ice Core Chronology 2005, GICC05, is extended back to 42 ka b2k (before 2000 AD), i.e. to the end of Greenland Stadial 11. The chronology is based on independent multi-parameter counting of annual layers using comprehensive high-resolution measurements available from the North Greenland Ice Core Project, NGRIP. These are measurements of visual stratigraphy, conductivity of the solid ice, electrolytical melt water conductivity and the concentration of Na⁺, Ca²⁺, SO₄²⁻, NO₃⁻, NH₄⁺. An uncertainty estimate of the time scale is obtained from identification of ‘uncertain’ annual layers, which are counted as 0.5±0.5 years. The sum of the uncertain annual layers, the so-called maximum counting error of the presented chronology ranges from 4% in the warm interstadial periods to 7% in the cold stadials. The annual accumulation rates of the stadials and interstadials are on average one-third and half of the present day values, respectively, and the onset of the Greenland Interstadials 2, 3, and 8, based on 20 year averaged δ¹⁸O values, are determined as 23,340, 27,780, and 38,220 yr b2k in GICC05.  相似文献   

Age, origin and geodynamic significance of plagiogranites in lherzolites and gabbros of the Piedmont-Ligurian ocean basin   总被引：11，自引：0，他引：11  

Laura Borsi  Urs Schrer  Laura Gaggero  Laura Crispini 《Earth and Planetary Science Letters》1996,140(1-4):227-241

U-Pb zircon dating, Sr-Nd isotope tracing and major/trace/RE element analyses were performed to constrain the age, origin and geodynamic significance of plagiogranites that intrude lherzolites and gabbros in the Ligurian Alps and the Northern Apennines. In addition, a host Fe-diorite was investigated. Samples from the Ligurian Alps were collected from the Voltri Group and the Sestri-Voltaggio Zone, whereas the plagiogranites from the Northern Apennines were taken in the Bracco unit. All these units have been affected by Alpine metamorphism reaching eclogite facies in the Voltri Group, blueschist degree in the Sestri Voltaggio samples, and prehnite-pumpellyite facies in the Bracco Unit, which has additionally been affected by rodingitization.

U-Pb zircon ages of 150 ± 1, 153 ± 1 and ≈ 156 Ma were obtained, respectively, for two plagiogranites and the host Fe-diorite in the Ligurian Alps, and an age of 153 ± 1 Ma was determined for the plagiogranite in Northern Apennines. Inherited components in zircon and initial Pb in plagioclase indicate mixing of variously differentiated basaltic magmas with small amounts of roughly 1.7–2.1 Ga old continental crust material. REE patterns in both the plagiogranites and the host diorite are characterized by high REE abundance, and moderate LREE enrichment. Nd isotopic compositions lie in the range of N-MORB sources, yielding initial epsilon Nd values between + 8.8 and + 9.7, whereas Sr is isotopically heterogeneous. The geochemical pattern of the plagiogranites and the host Fe-diorite requires melting of a MORB-type mantle source that experienced LREE enrichment shortly before melting. The most likely explanation for such enrichment is the injection of melts derived by small degrees of melting from an adjacent mantle region. The basaltic, LREE-enriched parent magmas generated from this enriched domain have probably undergone up to about 72% of low-pressure fractional crystallization prior to their emplacement into the gabbro-peridotite complex.

The 156–150 Ma magmatism occurred in close relation to normal faulting, sedimentation of breccias, and detachment of the mantle complex from its overlying continental crust, followed by exposure on the ocean floor. This tectono-magmatic event in the Ligurian Alps and the Northern Apennines reflects rifting of the Adriatic-Iberian continental plate segment, preceding wider opening of the Piedmont-Ligurian ocean basin and pillow basalt deposition.  相似文献   

Improving noble gas based paleoclimate reconstruction and groundwater dating using Ne/Ne ratios     

Frank Peeters  Urs Beyerle  Johannes Holocher  Rolf Kipfer 《Geochimica et cosmochimica acta》2003,67(4):587-600

The interpretation of noble gas concentrations in groundwater with respect to recharge temperature and fractionated excess gas leads to different results on paleo-climatic conditions and on residence times depending on the choice of the gas partitioning model. Two fractionation models for the gas excess are in use, one assuming partial re-equilibration of groundwater supersaturated by excess air (PR-model, Stute et al., 1995), the other assuming closed-system equilibration of groundwater with entrapped air (CE-model, Aeschbach-Hertig et al., 2000). In the example of the Continental Terminal aquifers in Niger, PR- and CE- model are both consistent with the data on elemental noble gas concentrations (Ne, Ar, Kr, and Xe). Only by including the isotope ratio ²⁰Ne/²²Ne it can be demonstrated that the PR-model has to be rejected and the CE-model should be applied to the data. In dating applications ³He of atmospheric origin (³He_atm) required to calculate ³H-³He water ages is commonly estimated from the Ne excess presuming that gas excess is unfractionated air (UA-model). Including in addition to the Ne concentration the ²⁰Ne/²²Ne ratio and the concentration of Ar enables a rigorous distinction between PR-, CE- and UA-model and a reliable determination of ³He_atm and of ³H-³He water ages.  相似文献   

Asteroseismology and interferometry     

M. S. Cunha  C. Aerts  J. Christensen-Dalsgaard  A. Baglin  L. Bigot  T. M. Brown  C. Catala  O. L. Creevey  A. Domiciano de Souza  P. Eggenberger  P. J. V. Garcia  F. Grundahl  P. Kervella  D. W. Kurtz  P. Mathias  A. Miglio  M. J. P. F. G. Monteiro  G. Perrin  F. P. Pijpers  D. Pourbaix  A. Quirrenbach  K. Rousselet-Perraut  T. C. Teixeira  F. Thévenin  M. J. Thompson 《Astronomy and Astrophysics Review》2007,14(3-4):217-360

Asteroseismology provides us with a unique opportunity to improve our understanding of stellar structure and evolution. Recent developments, including the first systematic studies of solar-like pulsators, have boosted the impact of this field of research within astrophysics and have led to a significant increase in the size of the research community. In the present paper we start by reviewing the basic observational and theoretical properties of classical and solar-like pulsators and present results from some of the most recent and outstanding studies of these stars. We centre our review on those classes of pulsators for which interferometric studies are expected to provide a significant input. We discuss current limitations to asteroseismic studies, including difficulties in mode identification and in the accurate determination of global parameters of pulsating stars, and, after a brief review of those aspects of interferometry that are most relevant in this context, anticipate how interferometric observations may contribute to overcome these limitations. Moreover, we present results of recent pilot studies of pulsating stars involving both asteroseismic and interferometric constraints and look into the future, summarizing ongoing efforts concerning the development of future instruments and satellite missions which are expected to have an impact in this field of research.  相似文献   

Fold interference patterns in the Late Palaeozoic Anti-Atlas belt of Morocco     

Caritg Séverine  Burkhard Martin  Ducommun Romain  Helg Urs  Kopp Lionel  Sue Christian 《地学学报》2004,16(1):27-37

We document two phases of folding within the central part of the Late Palaeozoic Anti‐Atlas chain of Morocco. A first generation of SW–NE folds involve a horizontal shortening of 10–20%, accommodated by polyharmonic buckle folding of contrasting wavelengths in Ordovician Jbel Bani quartzites and Devonian Jbel Rich carbonates. A second generation of folds with similar style and wavelengths in an E–W direction lead to complex interference patterns. Dome and basins are developed within the Jbel Rich and within Lower Cambrian dolomites. Both folding phases are related to thick‐skinned uplift of Precambrian basement in a Laramide style. In contrast to the typical Rocky Mountain foreland style, however, cover deformation in the Anti‐Atlas is mostly decoupled from the undying basement along thick incompetent horizons such as the Lower Cambrian Lie‐de‐Vin and Silurian shales.  相似文献