A noble gas and cosmogenic radionuclide analysis of two ordinary chondrites from Almahata Sitta     

Matthias M. M. MEIER  Kees C. WELTEN  Marc W. CAFFEE  Jon M. FRIEDRICH  Peter JENNISKENS  Kunihiko NISHIIZUMI  Muawia H. SHADDAD  Rainer WIELER 《Meteoritics & planetary science》2012,47(6):1075-1086

Abstract– We present the results of a noble gas (He, Ne, Ar) and cosmogenic radionuclide (¹⁰Be, ²⁶Al, ³⁶Cl) analysis of two chondritic fragments (#A100, L4 and #25, H5) found in the Almahata Sitta strewn field in Sudan. We confirm their earlier attribution to the same fall as the ureilites dominating the strewn field, based on the following findings: (1) both chondrite samples indicate a preatmospheric radius of approximately 300 g cm^?2, consistent with the preatmospheric size of asteroid 2008 TC₃ that produced the Almahata Sitta strewn field; (2) both have, within error, a ²¹Ne/²⁶Al‐based cosmic ray exposure age of approximately 20 Ma, identical to the reported ages of Almahata Sitta ureilites; (3) both exhibit hints of ureilitic Ar in the trapped component. We discuss a possible earlier irradiation phase for the two fragments of approximately 10–20 Ma, visible only in cosmogenic ³⁸Ar. We also discuss the approximately 3.8 Ga (⁴He) and approximately 4.6 Ga (⁴⁰Ar) gas retention ages, measured in both chondritic fragments. These imply that the two chondrite fragments were incorporated into the ureilite host early in solar system evolution, and that the parent asteroid from which 2008 TC₃ is derived has not experienced a large break‐up event in the last 3.8 Ga.  相似文献   

Moho Doublet in Southern Tibet and Its Tectonic Implication     

Junmeng Zhao  Rainer Kin  Xiaohui Yuan  Hongbing Liu  Shunping Pei  Prakash Kumar  Qimin Liu  Qiang Xu  Heng Zhang  Changhui Ju  Gong Deng  Caibayangzeng  Shuze Chen 《《地质学报》英文版》2018,92(Z1):43-44

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Streamline method for resolving sharp fronts for complex two-phase flow in porous media     

Ettore Vidotto  Rainer Helmig  Martin Schneider  Barbara Wohlmuth 《Computational Geosciences》2018,22(6):1487-1502

In this paper, we present a fast streamline-based numerical method for the two-phase flow equations in high-rate flooding scenarios for incompressible fluids in heterogeneous and anisotropic porous media. A fractional flow formulation is adopted and a discontinuous Galerkin method (DG) is employed to solve the pressure equation. Capillary effects can be neglected in high-rate flooding scenarios. This allows us to present an improved streamline approach in combination with the one-dimensional front tracking method to solve the transport equation. To handle the high computational costs of the DG approximation, domain decomposition is applied combined with an algebraic multigrid preconditioner to solve the linear system. Special care at the interior interfaces is required and the streamline tracer has to include a dynamic communication strategy. The method is validated in various two- and three-dimensional tests, where comparisons of the solutions in terms of approximation of flow front propagation with standard fully implicit finite-volume methods are provided.  相似文献   

Programme of the US.-Swiss conference on internal waves in geophysical contexts     

Rainer Beck 《地球物理与天体物理流体动力学》2013,107(1-3):3-4

Abstract

Evidence from radio polarization measurements is reviewed that indicates that most galactic magnetic field structures fall into one of two categories: axisymmetric spiral and bisymmetric spiral. The resultant challenges to dynamo theorists is stated. Estimates of the magnetic field strengths based on equipartition of field and cosmic ray energies are given, but deviations from equipartition are inferred. Possible goals for future research are suggested.  相似文献   

On the limits of using combined U-series/ESR method to date fossil teeth from two Early Pleistocene archaeological sites of the Orce area (Guadix-Baza basin,Spain)     

Mathieu Duval  Christophe Falguères  Jean-Jacques Bahain  Rainer Grün  Qingfeng Shao  Maxime Aubert  Jean-Michel Dolo  Jordi Agustí  Bienvenido Martínez-Navarro  Paul Palmqvist  Isidro Toro-Moyano 《Quaternary Research》2012,77(3):482-491

The combined U-series/electron spin resonance (ESR) dating method was applied to nine teeth from two Early Pleistocene archaeological sites located in the Orce area (Guadix-Baza Basin, Southern Spain): Fuente Nueva-3 (FN-3) and Barranco León (BL). The combination of biostratigraphy and magnetostratigraphy places both sites between the Olduvai and Jaramillo subchrons (1.78–1.07 Ma).Our results highlight the difficulty of dating such old sites and point out the limits of the combined U-series/ESR dating method based on the US model. We identified several sources of uncertainties that may lead to inaccurate age estimates. Seven samples could not be dated because the dental tissues had (²³⁰Th/²³⁴U) activity ratios higher than equilibrium, indicating that uranium had probably leached from these tissues. It was however possible to calculate numerical estimates for two of the teeth, both from FN-3. One yielded a Middle Pleistocene age that seems to be strongly underestimated; the other provided an age of 1.19 ± 0.21 Ma, in agreement with data obtained from independent methods. The latter result gives encouragement that there are samples that can be used for routine dating of old sites.  相似文献   

The abundance and isotopic composition of Cd in iron meteorites     

Thomas S. Kruijer  Peter Sprung  Thorsten Kleine  Ingo Leya  Rainer Wieler 《Meteoritics & planetary science》2013,48(12):2597-2607

Cadmium is a highly volatile element and its abundance in meteorites may help better understand volatility‐controlled processes in the solar nebula and on meteorite parent bodies. The large thermal neutron capture cross section of ¹¹³Cd suggests that Cd isotopes might be well suited to quantify neutron fluences in extraterrestrial materials. The aims of this study were (1) to evaluate the range and magnitude of Cd concentrations in magmatic iron meteorites, and (2) to assess the potential of Cd isotopes as a neutron dosimeter for iron meteorites. Our new Cd concentration data determined by isotope dilution demonstrate that Cd concentrations in iron meteorites are significantly lower than in some previous studies. In contrast to large systematic variations in the concentration of moderately volatile elements like Ga and Ge, there is neither systematic variation in Cd concentration amongst troilites, nor amongst metal phases of different iron meteorite groups. Instead, Cd is strongly depleted in all iron meteorite groups, implying that the parent bodies accreted well above the condensation temperature of Cd (i.e., ≈650 K) and thus incorporated only minimal amounts of highly volatile elements. No Cd isotope anomalies were found, whereas Pt and W isotope anomalies for the same iron meteorite samples indicate a significant fluence of epithermal and higher energetic neutrons. This observation demonstrates that owing to the high Fe concentrations in iron meteorites, neutron capture mainly occurs at epithermal and higher energies. The combined Cd‐Pt‐W isotope results from this study thus demonstrate that the relative magnitude of neutron capture‐induced isotope anomalies is strongly affected by the chemical composition of the irradiated material. The resulting low fluence of thermal neutrons in iron meteorites and their very low Cd concentrations make Cd isotopes unsuitable as a neutron dosimeter for iron meteorites.  相似文献   

Accretion and Early History of Planetesimals and Planets: The Noble Gas Record     

Rainer Wieler 《Earth, Moon, and Planets》2011,108(1):1-8

Some of the distinct noble gas “components” in meteorites represent a record of processes during and even before solar system formation. This record is difficult to interpret. Often, one of the major problems is to recognize whether a certain noble gas elemental and isotopic pattern has been established in a presolar epoch, later in the solar accretion disk, during meteorite parent body formation or finally as a result of metamorphism on a parent body. It would also appear that noble gases are a preferred tool to deduce the types of matter from which the Earth and other planets accreted—if the respective parent materials are present in our extraterrestrial sample collections at all. However, also this issue is unsettled. Noble gas isotopes originating from the decay of radioactive precursors allow us to study the early and later degassing history of terrestrial planets, although the interpretation often remains model-dependent. This contribution briefly reviews some of the fundamental aspects of the noble gas record in meteorites and planets.  相似文献   

Thermodynamic properties and equation of state of fcc aluminum and bcc iron, derived from a lattice vibrational method     

Michel H. G. Jacobs  Rainer Schmid-Fetzer 《Physics and Chemistry of Minerals》2010,37(10):721-739

We use a lattice vibrational technique to derive thermophysical and thermochemical properties of the pure elements aluminum and iron in pressure–temperature space. This semi-empirical technique is based on either the Mie–Grüneisen–Debye (MGD) approach or an extension of Kieffer’s model to incorporate details of the phonon spectrum. It includes treatment of intrinsic anharmonicity, electronic effects based on the free electron gas model, and magnetic effects based on the Calphad approach. We show that Keane’s equation of state for the static lattice is better suitable to represent thermodynamic data for aluminum from 1 bar to pressures in the multi-megabar region relative to Vinet’s universal and the Birch–Murnaghan equation of state. It appears that the MGD and Mie–Grüneisen–Kieffer approach produce similar results, but that the last one better represents heat capacity below room temperature. For iron we show that the high temperature behavior of thermal expansivity can be explained within the Calphad approach by a pressure-dependent Curie temperature with a slope between –1 and 0 K/GPa.  相似文献   

Symplectite formation during decompression induced garnet breakdown in lower crustal mafic granulite xenoliths: mechanisms and rates     

Júlia Dégi  Rainer Abart  Kálmán Török  Enikő Bali  Richard Wirth  Dieter Rhede 《Contributions to Mineralogy and Petrology》2010,159(3):293-314

The complex microstructure of kelyphitic rims around garnet in lower crustal garnet granulite xenoliths from the Bakony–Balaton Highland Volcanic Field, Central Pannonian Basin has been studied in order to identify controls on garnet breakdown. Symplectites comprised of a vermicular intergrowth of submicron sized anorthite, orthopyroxene and spinel replace garnet at a sharp reaction front. Based on element distribution maps the transformation of garnet to symplectite is isochemical. Phase diagram calculations indicate that this reaction was induced by a pressure decrease and/or a temperature increase. In site-specific TEM foils prepared by focused ion beam technique and oriented parallel and perpendicular to the reaction front 200 nm wide rods of anorthite and 20 nm wide rods of spinel are identified. The rods are oriented approximately perpendicular to the replacement front and are embedded in an orthopyroxene matrix. The regular spacing of the symplectite phases along the reaction front suggests that their growth is controlled by diffusion. The kinetics of symplectite formation has been modelled based on irreversible thermodynamics. During interaction of the xenolith with the host basalt the microstructure and chemistry of the An–Opx–Spl symplectite was significantly modified and it was partially replaced by an olivine bearing symplectite. In contrast to primary symplectite formation, these processes were metasomatic in nature including addition of sodium, titanium and some trace elements from the basaltic melt and can clearly be discerned from the garnet breakdown. Based on these observations it is inferred that symplectite formation took place within the deep crust during the extension of the Pannonian Basin between 15 and 30 km depth at high temperature (850–1,050°C) prior to the volcanic transport to the surface.  相似文献   

Determination of the crustal structure in southern Tibet by dispersion and amplitude analysis of Rayleigh waves   总被引：2，自引：0，他引：2  

N. Cotte  H. Pedersen  M. Campillo  J. Mars  J. F. Ni  R. Kind  E. Sandvol  & W. Zhao 《Geophysical Journal International》1999,138(3):809-819

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