Mineralogical control of selenium, tellurium and highly siderophile elements in the Earth’s mantle: Evidence from mineral separates of ultra-depleted mantle residues

International audienc

Reply to the comment on “A non-primitive origin of near-chondritic S–Se–Te ratios in mantle peridotites: Implications for the Earth's late accretionary history” by König S. et al. [Earth Planet. Sci. Lett. 385 (2014) 110–121]

International audienc

Siderite cannot be used as CO2 sensor for Archaean atmospheres

It was proposed to utilize siderite FeCO3 in mid to late Archaean Superior type banded as a proxy to constrain the CO2 partial pressure of Archaean atmospheres. Implicit in this proposition is that siderite was a primary carbonate mineral that crystallized directly from Fe2+ enriched Archaean seawater, in equilibrium with atmospheric CO2. To our knowledge that proposition has not been demonstrated to be valid. We test with water-gas exchange experiments under controlled CO2 partial pressures if siderite can be stabilized as a primary mineral in Fe2+ bearing seawater. Reduced seawater proxies enriched in Fe2+ and Mn2+ are equilibrated with reduced N2-CH4-CO2-H2 gas phases with variable CO2. The solid phases stabilized in Fe2+ enriched water compositions are amorphous ferrous iron hydroxy carbonates. Crystalline siderite FeCO3 is not found to be a stable phase. The phases precipitating from Mn2+ enriched water include crystalline rhodochrosite MnCO3 and possibly amorphous Mn-enriched phases. Based on these results we advise against using siderite in banded iron formations as a CO2 sensor for the Archaean atmosphere

A comparison of three statistical methods applied in the identification of eating patterns Comparação de três métodos estatísticos aplicados na identificação de padrões alimentares

This work aimed to compare the results of three statistical methods applied in the identification of dietary patterns. Data from 1,009 adults between the ages of 20 and 65 (339 males and 670 females) were collected in a population-based cross-sectional survey in the Metropolitan Region of Rio de Janeiro, Brazil. Information on food consumption was obtained using a semi-quantitative food frequency questionnaire. A factor analysis, cluster analysis, and reduced rank regression (RRR) analysis were applied to identify dietary patterns. The patterns identified by the three methods were similar. The factor analysis identified "mixed", "Western", and "traditional" eating patterns and explained 35% of the data variance. The cluster analysis identified "mixed" and "traditional" patterns. In the RRR, the consumption of carbohydrates and lipids were included as response variables and again "mixed" and "traditional" patterns were identified. Studies comparing these methods can help to inform decisions as to which procedures best suit a specific research scenario.<br>O objetivo deste estudo foi comparar três métodos estatísticos empregados na identificação de padrões alimentares. Foram utilizados dados de 1.009 adultos de 20 a 65 anos de idade (339 homens e 670 mulheres) coletados em estudo transversal de base populacional desenvolvido na Região Metropolitana do Rio de Janeiro, Brasil. Para a identificação de padrões alimentares foram aplicadas a análise fatorial, análise de cluster e a reduced rank regression analysis (RRR). Os três métodos identificaram padrões alimentares similares. A análise fatorial identificou os padrões "misto", "ocidental" e "tradicional", que explicaram 35% da variância total. Pela análise de cluster, foram identificados dois padrões "misto" e "tradicional". Para a RRR, os consumos de carboidratos e de lipídeos foram incluídos como variáveis respostas e também foram identificados os padrões "misto" e "tradicional". A comparação desses métodos auxilia na definição do procedimento mais adequado para um cenário de pesquisa específico