Trace element concentrations in zircons from ODP Holes 147-894G and 153-923A

The trace element compositions of Hadean zircons have been used in two ways to argue for the existence of Hadean continental crust. One argument is based on low crystallization temperatures of Hadean zircons that have been determined using a novel geothermometer based on the Ti content of zircons in equilibrium with rutile. The second argument is based on using the trace element abundances in zircons to calculate their parental melt compositions, especially the rare earth elements. Here we demonstrate that zircons that grow from a melt formed by basalt differentiation at modern mid-ocean ridges cannot be unambiguously distinguished from Hadean zircons on either of these grounds. Thus, we conclude that the trace element compositions of Hadean zircons are permissive of models that do not include the generation of continental crust in the Hadean.

Estrategias de reproducción social en grupos poblacionales que transitan de una economía formal a una economía solidaria : El caso de la Línea Sur de Río Negro en el Mercado de la Estepa 'Quimey Piuké'

Fil: Gallo, Josefina Mahuén. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

Geochemistry of basalts fropm DSDP Leg 65 basalts

Samples of basalt collected on Leg 65 near 22°N on the East Pacific Rise all display the depleted light rare-earth pattern of "normal" oceanic crust. Consequently the La/Ta ratio is close to 18, as opposed to the value of 9 associated with the flat or enriched patterns found along parts of the Mid-Atlantic Ridge and the Emperor Seamount chain. The Leg 65 samples are chemically similar to those from the CYAMEX area at 21 °N and to the Leg 54 samples from 9°N, suggesting homogeneity of the upper mantle under the northern part of the East Pacific Rise over a minimum distance of about 1500 km. The geochemistry of the rocks and their field relationships with respect to depth and distance from the axis of the Rise show no pattern of distribution linked to the degree of fractional crystallization and thus cast doubt on any possible model involving large, long-lived magma chambers at the axis of the Rise.

El cuerpo poseído como una forma de cuerpo sin órganos

El principal objetivo de este trabajo consiste en relacionar el concepto deleuziano de "cuerpo sin órganos" con el análisis que realiza Foucault, en Los anormales, del cuerpo poseído. Concretamente se intentará mostrar cómo es posible concebir al cuerpo poseído de Foucault como un cuerpo sin órganos deleuziano. El trabajo girará alrededor de tres grandes ejes: el organismo y el campo de intervención; la significancia y el dominio discursivo; la subjetivación y el saber. Finalmente se mencionará a la idea deleuziana de prudencia, entendida como arte común a los tres ejes.

Sedimentation at Manop Site H in the eastern equatorial Pacific

Gravity cores recovered from Manganese Nodule Project site H (6°33'N, 92°49'W) show marked downcore variations in the abundance of calcium carbonate, organic carbon, opal, manganese, and other components deposited over the past 400,000 years. Variations in the downcore abundance of organic carbon, which ranges from 0.2 to 1.0%, can be used to hindcast redox conditions in the surface sediments over this time. The results indicate that the depth to the manganese redox boundary varied from about 5 to 25 cm below the seafloor during four major cycles. Downcore variations in solid phase Mn, Ni, and Cu can be produced by such changes in redox conditions. A model which predicts that solid phase Mn can be trapped and buried when the Mn redox boundary migrates rapidly upward is consistent with the observed organic carbon and Mn records and supports the reconstructed redox variations. The history of redox variations at site H can be explained by changes with time in surface water productivity. Major productivity variations at the site occur over 100-kyr cycles, with relatively higher productivity occurring during glacial stages. Thus Quaternary climate changes influence surface water productivity, redox conditions in sediments, and the cycling of transition metals.

Estrategias de reproducción social en grupos poblacionales que transitan de una economía formal a una economía solidaria : El caso de la Línea Sur de Río Negro en el Mercado de la Estepa 'Quimey Piuké'

Fil: Gallo, Josefina Mahuén. Universidad Nacional de La Plata. Facultad de Humanidades y Ciencias de la Educación; Argentina.

El cuerpo poseído como una forma de cuerpo sin órganos

El principal objetivo de este trabajo consiste en relacionar el concepto deleuziano de "cuerpo sin órganos" con el análisis que realiza Foucault, en Los anormales, del cuerpo poseído. Concretamente se intentará mostrar cómo es posible concebir al cuerpo poseído de Foucault como un cuerpo sin órganos deleuziano. El trabajo girará alrededor de tres grandes ejes: el organismo y el campo de intervención; la significancia y el dominio discursivo; la subjetivación y el saber. Finalmente se mencionará a la idea deleuziana de prudencia, entendida como arte común a los tres ejes.