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Nancy L. Chabot Rachel H. Cueva Andrew W. Beck Richard D. Ash 《Meteoritics & planetary science》2020,55(4):726-743
Some of the defining characteristics of the IIG iron meteorite group are their high bulk P contents and massive, coarse schreibersite, which have been calculated to make up roughly 11–14 wt% of each specimen. In this study, we produced two data sets to investigate the formation of schreibersites in IIG irons: measurements of trace elements in the IIG iron meteorite Twannberg and experimental determinations of trace element partitioning into schreibersite. The schreibersite‐bearing experiments were conducted with schreibersite in equilibrium with a P‐rich melt and with bulk Ni contents ranging from 0 to 40 wt%. The partitioning behavior for the 20 elements measured in this study did not vary with Ni content. Comparison of the Twannberg measurements with the experimental results required a correction factor to account for the fact that the experiments were conducted in a simplified system that did not contain a solid metal phase. Previously determined solid metal/P‐rich melt partition coefficients were applied to infer schreibersite/solid metal partitioning behavior from the experiments, and once this correction was applied, the two data sets showed broad similarities between the schreibersite/solid metal distribution of elements. However, there were also differences noted, in particular between the Ni and P contents of the solid metal relative to the schreibersite inferred from the experiments compared to that measured in the Twannberg sample. These differences support previous interpretations that subsolidus schreibersite evolution has strongly influenced the Ni and P content now present in the solid metal phase of IIG irons. Quantitative attempts to match the IIG solid metal composition to that of late‐stage IIAB irons through subsolidus schreibersite growth were not successful, but qualitatively, this study corroborates the striking similarities between the IIAB and IIG groups, which are highly suggestive of a possible genetic link between the groups as has been previously proposed. 相似文献
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Geographies of age: thinking relationally 总被引:1,自引:0,他引:1
In contrast to recent treatment of other social identities, geographers' work on age still focuses disproportionately on the social-chronological margins – the very young and (to a far lesser extent) the very old – and rarely connects them directly. We outline the benefits of creating relational geographies of age, in order to build out from the recent explosion of children's geographies, and discuss three helpful concepts: intergenerationality, intersectionality and lifecourse. We suggest that participation provides one epistemological vehicle for getting beyond geographies which are mainly adults'. 相似文献
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Ever wanted to give school students or the public a closer look at the stars, without worrying about the vagaries of the UK weather? Paul Roche and Rachel Dodds from the Faulkes Telescope Project explain how you can do just that – without even leaving the classroom! 相似文献
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Peter J. ISAACSON Amit BASU SARBADHIKARI Carlé M. PIETERS Rachel L. KLIMA Takahiro HIROI Yang LIU Lawrence A. TAYLOR 《Meteoritics & planetary science》2011,46(2):228-251
The lunar rock and mineral characterization consortium (LRMCC) has conducted coordinated mineralogy/petrography/spectroscopy analyses of a suite of pristine lunar basalts. Four basalt slabs (two low‐Ti, two high‐Ti) and paired thin sections were analyzed. Thin sections were analyzed for mineralogy/petrography, while the slabs were used to prepare particulate separates of major mineral phases and bulk samples. Mineral separates and particulate bulk samples were crushed to controlled grain sizes and their reflectance spectra measured in the NASA RELAB at Brown University. The resulting data set provides an essential foundation for spectral mixing models, offers valuable endmember constraints for space weathering analyses, and represents critical new ground truth results for lunar science and exploration efforts. 相似文献
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Abstract– Pyroxenes are among the most common minerals in the solar system and are ideally suited for remote geochemical analysis because of the sensitivity of their distinctive spectra to mineral composition. Fe2+ is responsible for the dominant pyroxene absorptions in the visible and near‐infrared, but substitutions of other cations such as Ca2+ change the crystal structure and site geometries and thus the crystal field splitting energies of the Fe cations. To define spectral systematics resulting from major pyroxene cations (Ca2+, Mg2+, and Fe2+), we focus on a suite of pyroxenes synthesized with only Ca2+, Mg2+, and Fe2+ in the two octahedral sites, specifically examining the effect of Ca2+ on pyroxene absorption bands. The modified Gaussian model is used to deconvolve pyroxene spectra into component bands that can then be linked directly to crystal field absorptions. In orthopyroxenes and low‐Ca clinopyroxenes, Ca2+‐content has a strong and predictable effect on the positions of the absorption bands. At a threshold of Wo30, the crystal field environment stagnates and the M2 bands cease to change significantly as more Ca2+ is added. At Wo50, when most of the M2 sites are filled by Ca2+, band positions do not change drastically, although the presence and strengths of the 1 and 2 μm bands are affected by even trace amounts of Fe2+ in the M2 site. It is thus apparent that next‐nearest neighbors and the distortions they impose on the pyroxene lattice affect the electronic states around the Fe2+ cations and control absorption band properties. 相似文献
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Resource allocation for regional earthquake risk mitigation: a case study of Tehran,Iran 总被引:1,自引:1,他引:0
Pantea Vaziri Rachel A. Davidson Linda K. Nozick Mahmood Hosseini 《Natural Hazards》2010,53(3):527-546
This paper presents a new optimization model to help cities in seismically active developing countries decide (1) How much to spend on pre-earthquake mitigation versus waiting until after an event and paying for reconstruction or simply not rebuilding damaged buildings? (2) Which buildings to mitigate and how? and (3) Which buildings to reconstruct and how? It extends previously developed optimization models to consider the particular issues that arise in such countries. First, the model allows for the possibility that some damaged buildings will not be reconstructed immediately and keeps track of any lost building inventory. Second, buildings can be mitigated to, or when damaged, reconstructed to, any appropriate structural type and seismic design level. Finally, the model objectives include minimizing the chance of an extremely high death toll in any one earthquake and minimizing the average annual death toll across earthquakes. The model is illustrated through a case study analysis for Tehran, Iran. 相似文献
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