Noble gas investigations of lunar rocks 10017 and 10071     

P. Eberhardt  J. Geiss  H. Graf  N. Grögler  U. Krähenbühl  H. Schwaller  A. Stettler 《Geochimica et cosmochimica acta》1974,38(1):97-120

The noble gases He, Ne, Ar, Kr and Xe and also K and Ba were measured in the Apollo 11 igneous rocks 10017 and 10071, and in an ilmenite and two feldspar concentrates separated from rock 10071. Whole rock K/Ar ages of rocks 10017 and 10071 are (2350 ± 60) × 10⁶ yr and (2880 ± 60) × 10⁶ yr, respectively. The two feldspar concentrates of rock 10071 have distinctly higher ages: (3260 ± 60) × 10⁶ yr and (3350 ± 70) × 10⁶ yr. These ages are still 10 per cent lower than the Rb/Sr age obtained by Papanastassiouet al. (1970) and some Ar⁴⁰ diffusion loss must have occurred even in the relatively coarse-grained feldspar.The relative abundance patterns of spallation Ne, Ar, Kr and Xe are in agreement with the ratios predicted from meteoritic production rates. However, diffusion loss of spallation He³ is evident in the whole rock samples, and even more in the feldspar concentrates. The ilmenite shows little or no diffusion loss. The isotopic composition of spallation Kr and Xe is similar to the one observed in meteorites. Small, systematic differences in the spallation Kr spectra of rocks 10017 and 10071 are due to variations in the irradiation hardness (shielding). The Kr spallation spectra in the mineral concentrates are different from the whole rock spectra and also show individual variations, reflecting the differences in target element composition. The relative abundance of cosmic ray produced Xe¹³¹ differs by nearly 50 per cent in the two rocks. The other Xe isotopes show no variations of similar magnitude. The origin of the Xe¹³¹ yield variability is discussed.Kr⁸¹ was measured in all the samples investigated. The Kr⁸¹/Kr exposure ages of rocks 10017 and 10071 are (480 ± 25) × 10⁶ yr and (350 ± 15) × 10⁶ yr, respectively. Exposure ages derived from spallation Ne²¹, Ar³⁸, Kr⁸³ and Xe¹²⁶ are essentially in agreement with the Kr⁸¹/Kr ages. The age of rock 10071 might be somewhat low because of a possible recent exposure of our sample to solar flare particles.  相似文献   

AUDIO-VISUAL-TUTORIAL INSTRUCTION IN GEOGRAPHY     

Rainer R. Erhart 《The Professional geographer》1969,21(4):283-284

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A composite Fe,Ni‐FeS and enstatite‐forsterite‐diopside‐glass vitrophyre clast in the Larkman Nunatak 04316 aubrite: Origin by pyroclastic volcanism     

Klaus KEIL  Timothy J. McCOY  Lionel WILSON  Jean‐Alix BARRAT  Doug RUMBLE  Matthias M. M. MEIER  Rainer WIELER  Gary R. HUSS 《Meteoritics & planetary science》2011,46(11):1719-1741

Abstract– We studied the mineralogy, petrology, and bulk, trace element, oxygen, and noble gas isotopic compositions of a composite clast approximately 20 mm in diameter discovered in the Larkman Nunatak (LAR) 04316 aubrite regolith breccia. The clast consists of two lithologies: One is a quench‐textured intergrowth of troilite with spottily zoned metallic Fe,Ni which forms a dendritic or cellular structure. The approximately 30 μm spacings between the Fe,Ni arms yield an estimated cooling rate of this lithology of approximately 25–30 °C s^?1. The other is a quench‐textured enstatite‐forsterite‐diopside‐glass vitrophyre lithology. The composition of the clast suggests that it formed at an exceptionally high degree of partial melting, perhaps approaching complete melting, and that the melts from which the composite clast crystallized were quenched from a temperature of approximately 1380–1400 °C at a rate of approximately 25–30 °C s^?1. The association of the two lithologies in a composite clast allows, for the first time, an estimation of the cooling rate of a silicate vitrophyre in an aubrite of approximately 25–30 °C s^?1. While we cannot completely rule out an impact origin of the clast, we present what we consider is very strong evidence that this composite clast is one of the elusive pyroclasts produced during pyroclastic volcanism on the aubrite parent body ( Wilson and Keil 1991 ). We further suggest that this clast was not ejected into space but retained on the aubrite parent body by virtue of the relatively large size of the clast of approximately 20 mm. Our modeling, taking into account the size of the clast, suggests that the aubrite parent body must have been between approximately 40 and 100 km in diameter, and that the melt from which the clast crystallized must have contained an estimated maximum range of allowed volatile mass fractions between approximately 500 and approximately 4500 ppm.  相似文献   

Isotopic and elemental fractionation of solar wind implanted in the Genesis concentrator target characterized and quantified by noble gases     

Veronika S. HEBER  Roger C. WIENS  Amy J. G. JUREWICZ  Nadia VOGEL  Daniel B. REISENFELD  Heinrich BAUR  Kevin D. McKEEGAN  Rainer WIELER  Donald S. BURNETT 《Meteoritics & planetary science》2011,46(4):493-512

Abstract– We report concentrations and isotopic compositions of He, Ne, and Ar measured with high spatial resolution along a radial traverse of a silicon carbide (SiC) quadrant of the Genesis mission concentrator target. The Ne isotopic composition maps instrumental fractionation as a function of radial position in the target: the maximum observed isotopic fractionation is approximately 33‰ per mass unit between the center and periphery. The Ne fluence is enhanced by a factor of 43 at the target center and decreases to 5.5 times at the periphery relative to the bulk solar wind fluence. Neon isotopic profiles measured along all four arms of the “gold cross” mount which held the quadrants in the concentrator target demonstrate that the concentrator target was symmetrically irradiated during operation as designed. We used implantation experiments of Ne into SiC and gold to quantify backscatter loss and isotopic fractionation and compared measurements with numerical simulations from the code “stopping and range of ions in matter.” The ²⁰Ne fluence curve as a function of radial distance on the target may be used to construct concentration factors relative to bulk solar wind for accurate corrections for solar wind fluences of other light elements to be measured in the concentrator target. The Ne isotopic composition as a function of the radial distance in the SiC quadrant provides a correction for the instrumental mass‐dependent isotopic fractionation by the concentrator and can be used to correct measured solar wind oxygen and nitrogen isotopic compositions to obtain bulk solar wind isotopic compositions.  相似文献   

Halo streams in the solar neighborhood     

Rainer J. Klement 《Astronomy and Astrophysics Review》2010,18(4):567-594

The phase-space structure of our Galaxy holds the key to understand and reconstruct its formation. The ΛCDM model predicts a richly structured phase-space distribution of dark matter and (halo) stars, consisting of streams of particles torn from their progenitors during the process of hierarchical merging. While such streams quickly loose their spatial coherence in the process of phase mixing, the individual stars keep their common origin imprinted into their kinematic and chemical properties, allowing the recovery of the Galaxy’s individual “building blocks”. The field of Galactic Archeology has witnessed a dramatic boost over the last decade, thanks to the increasing quality and size of available data sets. This is especially true for the solar neighborhood, a volume of 1–2 kpc around the sun, where large scale surveys like SDSS/SEGUE continue to reveal the full 6D phase-space information of thousands of halo stars. In this review, I summarize the discoveries of stellar halo streams made so far and give a theoretical overview over the search strategies imployed. This article is intended as an introduction to researchers new to the field, but also as a reference illustrating the achievements made so far. I conclude that disentangling the individual fragments from which the Milky Way was built requires more precise data that will ultimately be delivered by the Gaia mission.  相似文献   

Redistribution of HFSE elements during rutile replacement by titanite   总被引：2，自引：0，他引：2  

Friedrich Lucassen  Peter Dulski  Rainer Abart  Gerhard Franz  Dieter Rhede  Rolf L. Romer 《Contributions to Mineralogy and Petrology》2010,160(2):279-295

Titanite growth at the expense of rutile during retrograde hydration of eclogite into amphibolite is a common phenomenon. We investigated an amphibolite sample from the Tromsø eclogite facies terrain in Northern Norway to gain insight into the trace element distribution between rutile and titanite during incomplete resorption of the rutile by titanite. Patchy compositional zoning of Al, Ti, and F in titanite relates to the presence of a fluid with variable Ti/Al and/or F during its growth. Laser ablation ICP–MS and electron microprobe data for high field strength elements (HFSE: Nb, Zr, Ta, and Hf) of rutile resorbed by titanite indicate a pronounced enrichment of these elements in the rim of a large single rutile crystal (~8 mm) and a systematic decrease towards uniform HFSE contents in the large core. HFSE contents of smaller rutile grains (~0.5 mm) and rutile inclusions (<100 μm) in the titanite overgrowth are similar or higher than in the rims of large rutile crystals. Element profiles from the rim inward demonstrate that HFSE enrichment in rutile is controlled by diffusion. HFSE ratios in diffusion-altered rutile show systematic variations compared with the uniform core composition of the large rutile. Modelling of Zr and Nb diffusion in rutile indicates that diffusion coefficients in rutile in fluid-dominated natural systems must be considerably higher than those determined experimentally at 1 bar in dry systems. Variations of HFSE contents in the newly formed titanite show no systematic spatial distribution. HFSE ratios in titanite and the rims of rutile are different, indicating different solid/fluid distribution coefficients in these minerals. Element fractionation by diffusion into the relict rutile and during fluid-mediated growth of new titanite could substantially change the HFSE budget of these minerals and could affect their use for geochemical tracing and other applications, such as Zr-based geothermobarometry.  相似文献   

Erratum to: Internally consistent geothermometers for garnet peridotites and pyroxenites     

Paolo Nimis  Herman Grütter 《Contributions to Mineralogy and Petrology》2010,159(3):429-436

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Nitrogen isotopes in the recent solar wind from the analysis of Genesis targets: Evidence for large scale isotope heterogeneity in the early solar system     

Bernard Marty  Laurent Zimmermann  Rainer Wieler  Donald L. Burnett  Peter Bochsler 《Geochimica et cosmochimica acta》2010,74(1):340-19141

We have analyzed nitrogen, neon and argon abundances and isotopic ratios in target material exposed in space for 27 months to solar wind (SW) irradiation during the Genesis mission. SW ions were extracted by sequential UV (193 nm) laser ablation of gold-plated material, purified separately in a dedicated line, and analyzed by gas source static mass spectrometry. We analyzed gold-covered stainless steel pieces from the Concentrator, a device that concentrated SW ions by a factor of up to 50. Despite extensive terrestrial N contamination, we could identify a non-terrestrial, ¹⁵N-depleted nitrogen end-member that points to a 40% depletion of ¹⁵N in solar-wind N relative to inner planets and meteorites, and define a composition for the present-day Sun (¹⁵N/¹⁴N = [2.26 ± 0.67] × 10⁻³, 2σ), which is indistinguishable from that of Jupiter’s atmosphere. These results indicate that the isotopic composition of nitrogen in the outer convective zone of the Sun has not changed through time, and is representative of the protosolar nebula. Large ¹⁵N enrichments due to e.g., irradiation, low temperature isotopic exchange, or contributions from ¹⁵N-rich presolar components, are therefore required to account for inner planet values.  相似文献   

Volume diffusion of Ytterbium in YAG: thin-film experiments and combined TEM–RBS analysis     

Katharina Marquardt  Elena Petrishcheva  Rainer Abart  Emmanuel Gardés  Richard Wirth  Ralf Dohmen  Hans-Werner Becker  Wilhelm Heinrich 《Physics and Chemistry of Minerals》2010,37(10):751-760

In this study, we address volume diffusion of ytterbium in yttrium aluminum garnet (YAG) using thin-film single crystal diffusion couples. We employ analytical transmission electron microscopy (ATEM) as a tool for combined microstructural and microchemical analysis and compare the results to Rutherford backscattering (RBS) analysis. Given the high spatial resolution of the method, we focus on microstructural changes of the thin-film diffusant source during the diffusion anneal. We evaluate the potential influence of the associated changes in its transport properties on the evolution of concentration profiles in the single crystal substrate. This approach allows us to test the reliability of determination of volume diffusion coefficients from thin-film diffusion experiments. We found that for the chosen experimental setting, the influence of thin-film re-crystallization is small when compared with the experimental uncertainty and good estimates for the volume diffusion coefficients of Yb in YAG can be obtained using standard assumptions. Both Yb-concentration profiles analyzed with ATEM and with RBS give similar results. At 1,450°C and 1 bar, we infer log D _Yb (m²/s) values of −19.37 ± 0.07 (TEM) and −19.84 ± 0.02 (RBS). Although the change in thin-film transport properties associated with successive crystallization during the diffusion anneal does not play a major role for our experimental setup, this effect cannot generally be ignored.  相似文献   

Numerical modeling of two-phase hysteresis combined with an interface condition for heterogeneous porous media     

Alexandros Papafotiou  Hussam Sheta  Rainer Helmig 《Computational Geosciences》2010,14(2):273-287

This paper presents a numerical implementation of two-phase capillary hysteresis and its combination with a capillary interface condition for the treatment of heterogeneities. The hysteresis concepts chosen in this work are first implemented in a node-centered FV discretization scheme and subsequently combined with the interface condition that predicts sharp saturation discontinuities at material interfaces, based on a pressure equilibrium concept. This approach allows for the approximation of history-dependent, and at the same time discontinuous, saturations at material interfaces. The resulting model provides a well-defined evolution of the hysteretic capillary pressure–saturation relationships at material interfaces that is independent of the grid spacing. As demonstrated with a simple 1-D example, this concept therefore offers the advantage that the solution of a two-phase flow problem involving hysteresis does not relate to the grid resolution at the material interfaces.  相似文献