Capturing an Evolving Nebular Environment: A Petrographic and Geochemical Study of a Type A, B & C CAI

Calcium, Aluminum-rich Inclusions (CAIs) were the first formed solids in our Solar System, with mineral assemblages reflecting the first phases predicted to condense out of a hot nebular gas of Solar composition. Geochemical, textural and crystallographic information in CAIs can be used to constrain the temperature, pressure, and composition (e.g., oxygen fugacity) of the gaseous reservoir(s) from which they formed, as well as any secondary (nebular and parent body) processes they underwent. Coordinated geochemical and textural analyses provide information on nebular conditions (i.e., astrophysical environments and dynamics of nebular gas reservoirs) in which these CAIs formed. In order to better understand the evolution of nebular reservoirs at the time of CAI formation, we analyzed a Type A, B and C CAI using Electron Probe Micro-Analyzer (EPMA) and Electron BackScatter Diffraction (EBSD) at NASA Johnson Space Center (JSC)

Distribution of Fe3+ and H in Minerals During Partial Melting and Metasomatism of Spinel Peridotite

Oxygen fugacity and water content are crucial parameters for many chemical and physical properties of the Earth's mantle, for example bearing on fluid type, melting initiation, and deformation. However, the exact behaviour of Fe3+ and H during melting and metasomatism is still under debate. Here, the Fe3+/Fe ratio (Mssbauer and EMP) and water content (FTIR) of peridotite minerals are examined in mantle xenoliths from Kilbourne Hole (KH), NM, and Dish Hill (DH), CA (USA). These spinel peridotites have compositions consistent with partial melting with variable degrees of metasomatism (undetectable to cryptic to modal). Pyroxenites also allow to examine melt-rock reactions. Bulk-rock Fe2O3 content of the KH peridotites correlates with indices of melting (positive with bulk-rock Al2O3 and Cpx Yb contents, and negative with spinel Cr#) confirming that Fe3+ behaves as an incompatible element during melting. Correlations of the Fe3+/Fe ratio of minerals with these indices, however, indicates that Fe3+ is incompatible in Cpx but compatible in Opx and spinel during melting. Water contents in olivine, Cpx and Opx from most KH peridotites can be explained by partial melting and correlate negatively with the Fe3+/Fe ratio of spinel and Opx but positively with that of Cpx. This indicates partial control of Fe3+ on the incorporation of H in pyroxene, but not related to a redox equilibrium in Cpx. The higher Fe3+/Fe ratio of spinel in the metasomatized KH and DH peridotites, and in the pyroxenites confirms that oxidation characterizes modal metasomatism. Metasomatism, however, is not necessarily accompanied by water addition

The Virtual-Spine Platform—Acquiring, visualizing, and analyzing individual sitting behavior

Back pain is a serious medical problem especially for those people sitting over long periods during their daily work. Here we present a system to help users monitoring and examining their sitting behavior. The Virtual-Spine Platform (VSP) is an integrated system consisting of a real-time body position monitoring module and a data visualization module to provide individualized, immediate, and accurate sitting behavior support. It provides a comprehensive spine movement analysis as well as accumulated data visualization to demonstrate behavior patterns within a certain period. The two modules are discussed in detail focusing on the design of the VSP system with adequate capacity for continuous monitoring and a web-based interactive data analysis method to visualize and compare the sitting behavior of different persons. The data was collected in an experiment with a small group of subjects. Using this method, the behavior of five subjects was evaluated over a working day, enabling inferences and suggestions for sitting improvements. The results from the accumulated data module were used to elucidate the basic function of body position recognition of the VSP. Finally, an expert user study was conducted to evaluate VSP and support future developments

Silicon isotopes in lunar rocks: Implications for the Moon's formation and the early history of the Earth

Silicon isotopic data from a range of lunar samples are presented to assess the degree of heterogeneity of the lunar mantle and its similarity to bulk silicate Earth (BSE). Multi-collector inductively-coupled-plasma mass spectrometry (MC-ICPMS) was used to analyse 24 samples, including both high and low-Ti basalts, as well as Highland anorthosites and picritic glasses, covering all the Apollo sample return missions. No systematic δ30Si differences are found between any of the bulk sample lithologies (±2σSD) (δ30SiLow-Ti basalt = −0.29 ± 0.06, δ30SiHigh-Ti basalt = −0.32 ± 0.09, δ30Silunar glass = −0.29 ± 0.05 and δ30SiHighland rocks = −0.27 ± 0.10). The average of the lunar samples is δ30Si = −0.29 ± 0.08 (2σSD), which is identical to the composition of BSE, δ30Si = −0.29 ± 0.08 (2σSD), from Savage et al. (2010). The BSE Si isotope composition is thought to be the result of Si partitioning between metal and silicate, and consequent isotopic fractionation during core formation. The Moon-forming impactor would not be expected to share that composition, because it is thought to have been relatively small (∼0.1 Earth masses) like Mars and formed under relatively low temperatures and pressures that are insufficient for Si to partition into the core. Therefore, the identical lunar and BSE Si isotope data show that Si isotopes, like those of oxygen, must have homogenised in the aftermath of the Moon-forming impact, if smooth particle hydrodynamic simulations of the Giant Impact are correct in showing that most lunar material should have originated from the impactor rather than the Earth. The data presented here are in agreement with other isotope systems and experimental studies that indicate that the majority of core formation happened early and before the Giant Impact. It has been predicted (Pahlevan et al., 2011) that the Moon and the BSE should show a ∼0.14‰ offset in δ30Si for the Moon to have an Fe/(Fe + Mg) ratio twice that of BSE. The current resolution and sample population size of the Si data for the Moon and Earth would allow such an offset to be detected. The fact that is it not observed can put constraints on the element ratios and lunar budgets as modelled by Pahlevan et al. (2011); in particular, it constrains the Fe/(Fe + Mg) ratio of the Moon to be only 1–1.3 BSE

Reseña histórica de la organización de todos los ayllus de Cañar tucayta

Profesor de Segunda Enseñanza en Ciencias de la Educación. Especialidad Historia y GeografíaCuenc

Silicon isotope homogeneity in the mantle

Thirty-five mafic and ultramafic rocks have been analysed for their silicon isotopic composition to very high precision with the aim of providing a robust average value for the silicate earth. This is of importance to studies using the difference between meteorite and terrestrial isotope composition to quantify silicon sequestration during core formation and, also, for understanding crustal processes. The δ³⁰Si values of the samples are more limited than previously reported, ranging between just -0.39 and -0.23‰ despite significant variations in chemical and other isotopic compositions. A hint of a trend exists between δ³⁰Si and both SiO₂ and Al₂O₃, which can be explained by concentration of the heavier isotopes in the melt as a function of silica polymerisation. Our best estimate for the δ³⁰Si of the bulk silicate earth (BSE) is -0.29 ± 0.08‰ (2 s.d.)

The effects of terrestrial weathering on samarium-neodymium isotopic composition of chondrites

International audienc

Silicon isotope homogeneity in the mantle

Thirty-five mafic and ultramafic rocks have been analysed for their silicon isotopic composition to very high precision with the aim of providing a robust average value for the silicate earth. This is of importance to studies using the difference between meteorite and terrestrial isotope composition to quantify silicon sequestration during core formation and, also, for understanding crustal processes. The δ30Si values of the samples are more limited than previously reported, ranging between just -0.39 and -0.23 despite significant variations in chemical and other isotopic compositions. A hint of a trend exists between δ30Si and both SiO2 and Al2O3, which can be explained by concentration of the heavier isotopes in the melt as a function of silica polymerisation. Our best estimate for the δ30Si of the bulk silicate earth (BSE) is -0.29±0.08 (2 s.d.). © 2010 Elsevier B.V