Chemical composition of Ninetyeast Ridge basalts

On Leg 121 of the Ocean Drilling Program, we recovered basaltic rocks from a total of three basement sites in the southern, central, and northern regions of Ninetyeast Ridge. These new sites complement the previous four basement holes drilled during Legs 22 and 26 of the Deep Sea Drilling Project, and confirm the predominantly tholeiitic, light rare earth element-enriched character of the basalts that cap the ridge. The basalts show marked iron enrichment; ferrobasalts occur at Sites 214 and 216 and oceanic andesites at Site 253. All of the basalts recovered during Leg 121 are altered, and range from aphyric olivine tholeiites (Site 756), to strongly plagioclase-phyric basalts (Site 757). Basalts from Site 758, which were clearly erupted in a submarine environment (pillow basalts are present in the section), are sparsely to strongly plagioclase-phyric. The basalts recovered at any one hole are isotopically homogeneous (except for the basalts from Site 758, which show a range of Pb isotopes), and it is possible to relate the magmas at any one site by high-level fractionation processes. However, there are significant variations in isotope ratios and highly incompatible element ratios between sites, which suggest that the mantle source for the ridge basalts was compositionally variable. Such variation, in view of the large volume of magmatic products that form the ridge system, is not surprising. There is not, however, a systematic variation in basalt composition along the ridge. We agree with previous models that relate Ninetyeast Ridge to a mantle plume in the southern Indian Ocean. The tholeiitic, iron-enriched, and voluminous character of the ridge basalts is typical of oceanic islands associated with plumes on or near a mid-ocean ridge (e.g., Iceland, Galapagos Islands, and St. Paul/Amsterdam islands). The absence of recovered alkalic suites is inconsistent with an intraplate setting, such as the Hawaiian Islands or Kerguelen Island. Thus, the major element data, like the gravity data, strongly suggest that the ridge was erupted on or very close to an active spreading center. Isotopically, the most likely plume that created the excess magmatism on the Ridge is the Kerguelen-Heard plume system, but the Ninetyeast Ridge basalts do not represent a simple mixing of the Kerguelen plume and mid-ocean Ninetyeast Ridge basalt mantle.

Gestión del conocimiento y del aprendizaje en la organización bibliotecaria

En este trabajo consideramos a la biblioteca como organización en la sociedad de la información y del conocimiento, por organizar y difundir la información registrada en diversos soportes. Hacemos análisis conceptuoso de términos específicos e interdisciplinarios incorporados a la Ciencia de la información, en el marco de la sociedad de la información y del conocimiento, tales como: dato, información, conocimiento, aprendizaje, gestión e innovación; integrados al proceso de la gestión del conocimiento y del aprendizaje en la organización bibliotecaria. Consideramos a la gestión del aprendizaje y del conocimiento un requisito insustituible en la formación y en el desarrollo de los recursos humanos, con la finalidad de producir cambios e innovación en los procesos de la organización bibliotecaria.

Eolian accumulation rates of ODP Leg 121 holes

The late Cenozoic history of eolian sedimentation in the eastern Indian Ocean was developed from samples recovered during drilling of Sites 752, 754, and 756. Temporal changes in the mass accumulation rate of eolian material reflect major climatic shifts in the southern African source region. A significant drop in dust mass flux values occurs near the end of the lower Oligocene. Younger sediments are characterized by a gradual reduction in dust accumulation rates until the middle Miocene after which values remain consistently low throughout the late Cenozoic, although a slight increase in eolian accumulation rate occurs near 2.5 Ma. This pattern of dust mass flux appears related to the supply of dust-sized particles in the source region and represents a shift in the climatic regime of southern Africa to increasingly more arid conditions throughout the late Cenozoic.

Age and chemical composition of magmatic rocks from the Belkovsky Island, New Siberian Islands

The study was inspired by information on Paleozoic andesites, dacites, and diabases on the Belkovsky Island in the 1974 geological survey reports used to reconstruct tectonic evolution of the continental block comprising the New Siberian Islands and the bordering shelf. We did not find felsic volcanics or Middle Paleozoic intrusions in the studied area of the island. Igneous rocks are mafic subvolcanic intrusions including dikes, randomly shaped bodies, explosion breccias, and peperites. They belong to the tholeiitic series and are similar to Siberian traps in petrography and trace-element compositions, with high LREE and LILE and prominent Nb negative anomalies. The island arc affinity is due to continental crust contamination of mantle magma and its long evolution in chambers at different depths. K-Ar biotite age (252+/-5 Ma) of magmatism indicates that it was coeval to the main stage of trap magmatism in the Siberian craton at the Permian-Triassic boundary. The terrane including the New Siberian Islands occurred on the periphery of the Siberian trap province where magmatism acted in rifting environment. Magma intruded into semiliquid wet sediments at shallow depths shortly after their deposition. Therefore, the exposed Paleozoic section in Belkovsky Island may include Permian or possibly Lower Triassic sediments of younger ages than it was believed earlier.

Gestión del conocimiento y del aprendizaje en la organización bibliotecaria

En este trabajo consideramos a la biblioteca como organización en la sociedad de la información y del conocimiento, por organizar y difundir la información registrada en diversos soportes. Hacemos análisis conceptuoso de términos específicos e interdisciplinarios incorporados a la Ciencia de la información, en el marco de la sociedad de la información y del conocimiento, tales como: dato, información, conocimiento, aprendizaje, gestión e innovación; integrados al proceso de la gestión del conocimiento y del aprendizaje en la organización bibliotecaria. Consideramos a la gestión del aprendizaje y del conocimiento un requisito insustituible en la formación y en el desarrollo de los recursos humanos, con la finalidad de producir cambios e innovación en los procesos de la organización bibliotecaria.

Politización, participación política y acción colectiva : La emergencia y conformación de la Asamblea Permanente por los Derechos de la Niñez en la ciudad de La Plata en el año 2008

La presente tesina intenta reconstruir el proceso de emergencia y conformación de un actor colectivo en el marco de la politización de una problemática social. Específicamente, se abordará la constitución de la Asamblea Permanente por los Derechos de la Niñez y la politización de la problemática de la niñez en situación de calle en la ciudad de La Plata, a mediados del año 2008. En el marco de un escenario de conflicto en el cual un conjunto de chicos en situación de calle que estaban viviendo en plaza San Martín, eran visibilizados por los medios de comunicación locales como una banda delictiva, comienzan a llevarse a cabo una serie de acciones colectivas con el objetivo de demandar soluciones para aquel grupo. Es así que el objetivo de la tesina es, en primer lugar, poder dar cuenta de dicho escenario, identificando los diferentes actores involucrados y las acciones desplegadas, así como también, examinar los sentidos y significados puestos en juego en las mismas. También, se intentará indagar en cuáles fueron las acciones, los discursos y los sujetos que generaron la politización de dicha problemática social. En este sentido, se abordarán distintas trayectorias militantes de algunos integrantes del proceso para dar cuenta de experiencias de politización desde una clave individual. Se considera, por último, que el caso es relevante ya que permite indagar en cómo emerge un actor social en el marco de un escenario de conflicto a partir del involucramiento y desarrollo de una gama de procesos sociales, diferentes actores y formas de acción

Rare earth elements of modern seeps from the Gulf of Mexico, the Black Sea, and the Congo Fan

At marine seeps, methane is microbially oxidized resulting in the precipitation of carbonates close to the seafloor. Methane oxidation leads to sulfate depletion in sediment pore water, which induces a change in redox conditions. Rare earth element (REE) patterns of authigenic carbonate phases collected from modern seeps of the Gulf of Mexico, the Black Sea, and the Congo Fan were analyzed. Different carbonate minerals including aragonite and calcite with different crystal habits have been selected for analysis. Total REE content (SumREE) of seep carbonates varies widely, from 0.1 ppm to 42.5 ppm, but a common trend is that the SumREE in microcrystalline phases is higher than that of the associated later phases including micospar, sparite and blocky cement, suggesting that SumREE may be a function of diagenesis. The shale-normalized REE patterns of the seep carbonates often show different Ce anomalies even in samples from a specific site, suggesting that the formation conditions of seep carbonates are variable and complex. Overall, our results show that apart from anoxic, oxic conditions are at least temporarily common in seep environments.