Geochemistry of North Atlantic Igneous Province basalts

New Sr-Nd-Pb-Hf data require the existence of at least four mantle components in the genesis of basalts from the the North Atlantic Igneous Province (NAIP): (1) one (or more likely a small range of) enriched component(s) within the Iceland plume, (2) a depleted component within the Iceland plume (distinct from the shallow N-MORB source), (3) a depleted sheath surrounding the plume and (4) shallow N-MORB source mantle. These components have been available since the major phase of igneous activity associated with plume head impact during Paleogene times. In Hf-Nd isotope space, samples from Iceland, DSDP Leg 49 (Sites 407, 408 and 409), ODP Legs 152 and 163 (southeast Greenland margin), the Reykjanes Ridge, Kolbeinsey Ridge and DSDP Leg 38 (Site 348) define fields that are oblique to the main ocean island basalt array and extend toward a component with higher 176Hf/177Hf than the N-MORB source available prior to arrival of the plume, as indicated by the compositions of Cretaceous basalts from Goban Spur (~95 Ma). Aside from Goban Spur, only basalts from Hatton Bank on the oceanward side of the Rockall Plateau (DSDP Leg 81) lie consistently within the field of N-MORB, which indicates that the compositional influence of the plume did not reach this far south and east ~55 Ma ago. Thus, Hf-Nd isotope systematics are consistent with previous studies which indicate that shallow MORB-source mantle does not represent the depleted component within the Iceland plume (Thirlwall, J. Geol. Soc. London 152 (1995) 991-996; Hards et al., J. Geol. Soc. London 152 (1995) 1003-1009; Fitton et al., 1997 doi:10.1016/S0012-821X(97)00170-2). They also indicate that the depleted component is a long-lived and intrinsic feature of the Iceland plume, generated during an ancient melting event in which a mineral (such as garnet) with a high Lu/Hf was a residual phase. Collectively, these data suggest a model for the Iceland plume in which a heterogeneous core, derived from the lower mantle, consists of 'enriched' streaks or blobs dispersed in a more depleted matrix. A distinguishing feature of both the enriched and depleted components is high Nb/Y for a given Zr/Y (i.e. positive DeltaNb), but the enriched component has higher Sr and Pb isotope ratios, combined with lower epsilon-Nd and epsilon-Hf. This heterogeneous core is surrounded by a sheath of depleted material, similar to the depleted component of the Iceland plume in its epsilon-Nd and epsilon-Hf, but with lower 87Sr/86Sr, 208Pb/204Pb and negative DeltaNb; this material was probably entrained from near the 670 km discontinuity when the plume stalled at the boundary between the upper and lower mantle. The plume sheath displaced more normal MORB asthenosphere (distinguished by its lower epsilon-Hf for a given epsilon-Nd or Zr/Nb ratio), which existed in the North Atlantic prior to plume impact. Preliminary data on MORBs from near the Azores plume suggest that much of the North Atlantic may be 'polluted' not only by enriched plume material but also by depleted material similar to the Iceland plume sheath. If this hypothesis is correct, it may provide a general explanation for some of the compositional diversity and variations in inferred depth of melting (Klein and Langmuir, 1987 doi:10.1029/JB092iB08p08089) along the MAR in the North Atlantic.

Whole rock and Cr-rich spinel geochemistry of ODP Legs 152 and 163 and DSDP Hole 38-338 samples

Coring during Ocean Drilling Program and Deep Sea Drilling Project Legs 163, 152, 104, 81, and 38 recovered sequences of altered basalt from North Atlantic seaward-dipping reflector sequences (SDRS) erupted during the initial rifting of Greenland from northern Europe and likely associated with excessive mantle temperatures caused by an impacting mantle plume head. Cr-rich spinel is found abundantly as inclusions and groundmass crystals within the olivine-rich lavas of Hole 917A (Leg 152) cored into the Southeast Greenland SDRS, but only rarely as inclusions within plagioclase in the lavas of the Vøring Plateau SDRS, and it is absent from other cored SDRS lavas from the Rockall Plateau and Southeast Greenland. Eruptive melt compositions determined from inferred, thermodynamically-defined, spinel-melt exchange equilibria indicate that the most primitive melts represented by Hole 917A basalts have Mg/(Mg + Fe2+) at least as high as 0.70 and approach near-primary mantle melt compositions. In contrast, Cr-rich spinels from Hole 338 (Leg 38) lavas on the Vøring Plateau SDRS give evidence for melt with Mg/(Mg + Fe2+) only as high as 0.64. This study underlines that primitive melts similar to those from Hole 917A comprise only a small fraction of the eruptive North Atlantic SDRS melts, and that most SDRS basalts were, in fact, too evolved to have precipitated Cr-rich spinel, with true melt Mg/(Mg + Fe2+) likely below 0.60. The evolved nature of the SDRS basalts implies large amounts of fractionation at the base of the crust or deep within it, consistent with seismic results that indicate an abnormally thick Layer 3 underlying the SDRS.

Sapientia, 1984, Vol. XXXIX, nº 152 (número completo)

Contenido: Aspectos fundamentales del conocimiento humano. II. El conocimiento intelectivo / Octavio N. Derisi -- El ser y los entes / Octavio N. Derisi -- Poder y persona en la sociedad humana / Pedro E. Baquero Lazcano -- Refutaciones actuales de la "falacia naturalista" / Carlos I. Massini -- La sabiduría en Santo Tomás : ascensión a la intimidad con Dios por la participación de la verdad y el amor / Ciro Schmidt Andrade -- Consideraciones en torno al tema de los valores / Mieczyslaw Gogacz -- Notas y comentarios -- Bibliografía

Diário da Constituinte [gravação de vídeo] : [programa n. 152]

O anteprojeto do Relator Bernardo Cabral (PMDB-AM) estabelece que os cargos de confiança no serviço público não poderão ser preenchidos por parentes até o segundo grau de parentesco. A Deputada Beth Azize (PSB-AM) declara que o dispositivo, se aprovado e aplicado, acabará com a prática do nepotismo. A Deputada Dirce Tutu Quadros (PTB-SP) acredita ser uma forma de moralizar o país, de acabar com o empreguismo, que está tornando o país deficitário. O Deputado Maluly Neto (PFL-SP) julga que o artigo não deve constar na Constituição por ser matéria de lei ordinária. O Deputado Felipe Mendes (PDS-PI) informa que não é esse tipo de dispositivo que vai resolver a questão do empreguismo e diz que a nova Constituição deve disciplinar os gastos públicos, na área do funcionalismo, para remunerar melhor aqueles que efetivamente trabalham. Na sessão O Povo Pergunta, menor gostaria de saber quais são os direitos das crianças. O Deputado Cláudio Ávila da Silva (PFL-SC) responde que chegou o momento de retomar a possibilidade de dar aos jovens e às crianças os seus direitos básicos, dentre os quais está a educação. O Deputado Álvaro Vale (PL-RJ) quer mudar as normas da Assembleia Nacional Constituinte e propõe que cento e oitenta e oito constituintes se unam para sugerir um projeto próprio de Constituição, ou emendar capítulos inteiros do projeto do Relator da Comissão de Sistematização. O Deputado Bernardo Cabral (PMDB-AM) é contra a mudança do Regimento Interno.

Keys to the larvae of the species of the genera Diamesa, Eukiefferiella, Orthocladius, Cricotopus, Psectrocladius and Chaetocladius. [Translation from: Larvae and pupae of midges of the subfamily Orthocladiinae of the fauna of the USSR (Diptera, Chironomidae = Tendipedidae) (ed. V.Y. Pankratova) p76-8,151-152,173-174,188-189. Leningrad, Nauka, 1970. ]

Eudiaptomus vulgaris Schmeil is the most abundant copepod in Lake Maggiore and forms also, in respect to other entomostraca, the most important element, through its average biomass and because it is fairly numerous throughout the year. Plankton samples collected in a systematic and quantitative way, gave the opportunity to study some aspects of the dynamics of the population of this copepod, in safety in view of the uncertainty which in this kind of study can ensue when samples are taken only at a single station - in consequence of the changes in size of population between different water masses. The results of the biometrical observations are of the population of Eudiaptomus vulgaris is presented.

Levantamento exploratório-reconhecimento de alta intensidade e aptidão agrícola dos solos da área compreendida entre os km 81 e 152 da Rodovia Santarém-Cuiabá e o Rio Curua-Una.

Foram estudados os solos de uma area com 390.000 ha, situada a margem esquerda da Rodovia Santarem-Cuiaba, num trecho compreendido entre a cidade de Santarem e a Ruropolis Presidente Medici, no Estado do Para, com o objetivo de fornecer elementos basicos ao planejamento para ocupacao da area, atraves projetos de colonizacao. O trabalho constou do levantamento pedologico e posterior determinacao da aptidao agricola dos diferentes solos identificados e mapeados. Predominam na area os Latossolos e os podzolicos, ocorrendo em pequenas proporcoes as areias Quartzosas. As principais limitacoes se referem a fertilidade e a deficiencia de agua, enquanto que nos podzolicos, porquanto existam as limitacoes supracitadas, e o relevo que exerce em sua maioria, o principal papel de limitacoes das terras para o aproveitamento agropastoril. De acordo com o sistema de aptidao agricola adotado, os Latossolos, apesar de apresentarem baixa fertilidade e alta saturacao de aluminio, dada as suas propriedades fisicas, podem ser utilizados em empreendimentos agropecuarios com bons resultados, assim como os Podzolicos de relevo forte ondulado, recomenda-se a sua utilizacao para pastagem plantada ou silvicultura, e, para as Areais Quartzosas a melhor indicacao e a silvicultura.