Strontium concentrations and isotopic compositions of anhydrites from the TAG active mound

Sr isotope analyses have been conducted on anhydrite samples from the TAG (Trans-Atlantic Geotraverse) active hydrothermal mound (26°08?N, Mid-Atlantic Ridge) that have previously been shown to exhibit two distinct patterns of REE behavior when normalized to TAG end-member hydrothermal fluid. Despite differences in REE patterns, the Sr isotope data indicate that all the anhydrites precipitated from fluids with a similar range of hydrothermal fluid and seawater components, and all but one were seawater-dominated (52%-75%). Speciation calculations using the EQ3/6 software package for geochemical modeling of aqueous systems suggest that the REE complexation behavior in different fluid mixing scenarios can explain the variations in the REE patterns. Anhydrites that exhibit relatively flat REE patterns [(La_bs)/(Yb_bs) = 0.8-2.0; subscript bs indicates normalization to end-member black smoker hydrothermal fluid] and a small or no Eu anomaly [(Eu_bs)/(Eu*_bs) = 0.8-2.0] are inferred to have precipitated from mixes of end-member hydrothermal fluid and cold seawater. REE complexes with hard ligands (e.g., fluoride and chloride) are less stable at low temperatures and trivalent Eu has an ionic radius similar to that of Ca2+ and the other REE, and so they behave coherently. In contrast, anhydrites that exhibit slight LREE-depletion [(La_bs)/(Yb_bs) = 0.4-1.4] and a distinct negative anomaly [(Eu_bs)/(Eu*_bs) = 0.2-0.8] are inferred to have precipitated from mixes of end-member hydrothermal fluid and conductively heated seawater. The LREE depletion results from the presence of very stable LREE chloro-complexes that effectively limit the availability of the LREE for partitioning into anhydrite. Above 250°C, Eu is present only in divalent form as chloride complexes, and discrimination against Eu2+ is likely due to both the mismatch in ionic radii between Eu2+ and Ca2+, and the strong chloro-complexation of divalent Eu which promotes stability in the fluid and inhibits partitioning of Eu2+ into precipitating anhydrite. These variations in REE behavior attest to rapid fluctuations in thermal regime, fluid flow and mixing in the subsurface of the TAG mound that give rise to heterogeneity in the formation conditions of individual anhydrite crystals.

Mapping of large scale 158 mu m [CII] line emission: Orion A

We present the first results of an observational programme undertaken to map the fine structure line emission of singly ionized carbon ([ CII] 157 : 7409 mum) over extended regions using a Fabry Perot spectrometer newly installed at the focal plane of a 100 cm balloon- borne far- infrared telescope. This new combination of instruments has a velocity resolution of similar to 200 km s(-1) and an angular resolution of 1.'5. During the first flight, an area of 30' x 15' in Orion A was mapped. These observations extend over a larger area than previous observations, the map is fully sampled and the spectral scanning method used enables reliable estimation of the continuum emission at frequencies adjacent to the [ CII] line. The total [ CII] line luminosity, calculated by considering up to 20% of the maximum line intensity is 0.04% of the luminosity of the far- infrared continuum. We have compared the [ CII] intensity distribution with the velocity- integrated intensity distributions of (CO)-C-13(1- 0), CI(1- 0) and CO( 3- 2) from the literature. Comparison of the [ CII], [ CI] and the radio continuum intensity distributions indicates that the largescale [ CII] emission originates mainly from the neutral gas, except at the position of M 43, where no [ CI] emission corresponding to the [ CII] emission is seen. Substantial part of the [ CII] emission from here originates from the ionized gas. The observed line intensities and ratios have been analyzed using the PDR models by Kaufman et al. ( 1999) to derive the incident UV flux and volume density at a few selected positions. The models reproduce the observations reasonably well at most positions excepting the [ CII] peak ( which coincides with the position of theta(1) Ori C). Possible reason for the failure could be the simplifying assumption of a homogeneous plane parallel slab in place of a more complicated geometry.

Sapientia, 1985, Vol. XL, nº 158 (número completo)

Contenido: La verdad (IV). El significado y la trascendencia de la verdad para el perfeccionamiento humano / Octavio N. Derisi -- El entender como perfección : la operación inmanente / J. L. González Alió -- Conocimiento y causalidad / Mario E. Sacchi -- Notas y comentarios -- Bibliografía

Diário da Constituinte [gravação de vídeo] : [programa n. 158]

Os Deputados Carlos Alberto de Oliveira Caó (PDT-RJ), Edmilson Valentim (PC do B-RJ) e Benedita da Silva (PT-RJ) acertaram com o Deputado Bernardo Cabral, Relator da Comissão de Sistematização da Assembleia Nacional Constituinte (ANC), a fixação de princípio constitucional contra a discriminação racial. O Deputado Carlos Alberto de Oliveira Caó (PDT-RJ) esclarece que foram apresentadas duas solicitações: definir o racismo como crime inafiançável e estabelecer que o governo brasileiro não mantenha nenhum tipo de relação, seja diplomática ou comercial, com países que adotam políticas segregacionistas. Altair Torres, Diretor do Instituto de Pesquisas da Cultura Negra, declara que considera importantíssima a definição do racismo como crime inafiançável. A Deputada Benedita da Silva (PT-RJ) diz que houve avanços, como a garantia de educação com respeito a pluralidade étnica, a restituição de terras aos negros remanescentes de quilombos e o estabelecimento da igualdade em relação aos salários. Causa polêmica a proposta do Deputado Asdrubal Bentes (PMDB-PA) que proíbe maiores de setenta anos de se candidatarem a cargos eletivos. O Deputado Sotero Cunha (PDC-RS) discorda da proposta, pois considera que uma pessoa aos setenta anos de idade ainda tem condições de realizar um trabalho legislativo. O Deputado Paulo Delgado (PT-MG) considera a proposta uma discriminação e diz que precisamos impedir a elegibilidade de políticos corruptos. O Deputado Furtado Leite (PFL-CE) defende a tese de que experiência ninguém deve jogar fora e que, aos setenta anos, qualquer pessoa tem condições de dar uma grande contribuição.