Geochemistry at DSDP Leg 70 Holes

A total of 32 holes at five sites near 1°N, 86°W drilled on Deep Sea Drilling Project (DSDP) Leg 70 (November- December 1979) provide unique data on the origin of the hydrothermal mounds on the southern flank of the Galapagos Spreading Center. Hydrothermal sediments, primarily Mn-oxide and nontronite, are restricted to the immediate vicinity of the mounds (< 100 m) and are probably formed by the interaction of upward-percolating hydrothermal solutions with seawater and pelagic sediments above locally permeable zones of ocean crust. Mounds as high as 25 meters form in less than a few hundred thousand years, and geothermal and geochemical gradients indicate that they are actively forming today. The lack of alteration of upper basement rocks directly below the mounds and throughout the Galapagos region indicates that the source of the hydrothermal solutions is deeper in the crust.

Composition of hydrothermal manganese oxide deposits from Galapagos mounds, DSDP Leg 70, Hole 509B

During DSDP Leg 70, a 1.60 m thick manganese oxide layer was sampled in hole 509B. This deposit is formed of alternating layers of hard plates of pure todorokite, about 2 mm thick, and of a more powdery material deeply impregnated with manganese oxide, about 3 mm thick. A SEM study of the plates and the associated powder shows that the powdery material is a transformation of a pre-existing sediment, while the plates are a direct precipitation from a hydrothermal solution. The uranium series disequilibrium method was used to determine the ages of the plates. They are found to be in good chronological sequence and in accordance with the sedimentation rate of the area (4.9 cm/10^3 years) which implies that they have been formed at the sediment-seawater interface during a pulsed injection of hydrothermal solution. The powder presents systematically an "older age" which is explained by a slowing down of the injection while the normal sediment settles; the older age is due to the 230Th excess of the sediment.

Radiochemistry at DSDP Leg 54 and 70 Holes

Use of the hydraulic piston corer during DSDP Leg 70 in the Galapagos mounds area allowed recovery of an undisturbed sedimentary sequence down to the basement. It thus became possible to establish the chronology of different events. Several holes on and off the mounds were studied, using uranium series disequilibrium methods of age determination and oxygen isotope stratigraphy. The following sequence was thereby established: 1) From 600,000 to 300,000 years ago there was normal pelagic sedimentation, with an injection of uranium-rich solution, probably of hydrothermal origin, between 400,000 and 300,000 years ago. 2) From 300,000 to 90,000 years ago, nontronitic clay formed, replacing a pre-existing sediment. 3) From 60,000 to 20,000 years ago, manganese oxide deposits formed, probably also replacing pre-existing sediments. 4) About 19,000 years ago there occurred a uranium injection from seawater, attributed to the end of the hydrothermal circulation. In some holes, especially Hole 424, Leg 54, younger manganese oxides have been found, indicating that some mounds may be presently active.

Concentration and isotope composition of sulphur in sediments and pore water at DSDP Leg 70 Holes

Data obtained while investigating the mounds area near the Galapagos Spreading Center demonstrate the direct influence of solutions derived from the interaction of seawater and young oceanic crust on the sedimentary cover. Investigation of metalliferous sediments from the mid-oceanic ridges, the Galapagos mounds, and the FAMOUS-area zone formations have shown that this influence and the resulting products are dependent on composition, temperature, and conditions of solution input. The study of sulfur in upwardly migrating solutions and the interaction of these solutions with sediments is of great interest. Investigations of different types of hydrothermally derived formations (Edmond, et al., 1979; Spiess et al., 1980; Styrt et al., 1981; Rosanova 1976; Grinenko et al., 1978) have shown the significant role of sulfur-bearing minerals in deposits formed from hightemperature solutions. In contrast, the addition of hydrothermal sulfur is negligible in those metalliferous sediments that precipitated as a result of the interaction between the solutions and open seawater (Bonatti et al., 1972, 1976; Gordeev et al., 1979; Migdisov, Bogdanov, et al., 1979). For example, sulfides are absent in clearly oxidized metalliferous sediments from the East Pacific Rise (EPR). Barite sulfur from these sediments is identical with seawater sulfate sulfur in isotope composition (Grinenko et al., 1978). Gurvich and Bogdanov (1977) have suggested that barium from EPR metalliferous sediments results completely from biological activity and from the components of ocean waters. Edmond et al. (1979) report that low-temperature springs from the Galapagos Rift axis contain two types of solutions: those with and those without H2S.

Chemical composition and sulfur-isotope ratios in DSDP Legs 69-and 70

As part of the geochemical-petrological study of basalts recovered from DSDP Hole 504B (Leg 70) on the southern flank of the Costa Rica Rift, we investigated specially the relationships between the distribution and isotopic composition of sulfur of scattered and vein sulfides on the one hand, and the observed pattern and processes of secondary alterations on the other. The following groups of observations are essential: (1) variations in the contents and isotopic composition of sulfur of different forms of sulfides are clearly interrelated and are observed solely in porous horizons established on the basis of detailed geophysical experiments; (2) the enrichment of sulfides in the light sulfur isotope decreases from the upper to the lower horizons, and within horizons in the direction of the less-altered rock; (3) the increase of d34S values of scattered sulfides in individual permeable zones parallels a decrease in the degree of iron oxidation in the contents of crystallization water, and in the concentrations of Mg, K, and Li in the rock.

Major, trace and rare earth elements and minerals at DSDP Legs 69-70 Holes

We obtained major and trace element data on 113 samples from basalts drilled during DSDP Legs 69 and 70 in the Costa Rica Rift area. The majority have major and trace element characteristics typical of ocean-ridge tholeiities. Most of the basalts are relatively MgO rich (MgO > 8 wt.%) and have Mg values (MgO/MgO + 0.85FeO x 100) of about 53, characteristics that clearly indicate that the various magmas underwent only a small amount of crystal fractionation before being erupted onto the seafloor. According to their normative mineralogies, the rocks are olivine tholeiites. A few samples plot close to the diopside-hypersthene join of the projected basalt tetrahedron. Except for basalts from two thin intervals in Hole 504B, which differ significantly from all the other basalts of the hole, practically no chemical downhole variation could be established. In the two exceptional intervals, both TiO2 and P2O5 contents are markedly enriched among the major oxides. The trace elements in these intervals are distinguished by relatively high contents of magmatophile elements and have flat to enriched chondrite-normalized distribution patterns of light rare earth elements (LREE). Most of the rocks outside these intervals are strongly depleted in large-ionlithophile (LIL) elements and LREE. We offer no satisfactory hypothesis for the origin of these basalts at this time. They might have originated within pockets of mantle materials that were more primitive than the LIL-element-depleted magmas that were the source of the other basalts. A significant change with depth in the type of alteration occurs in the 561 meters of basalt cored in Hole 504B. According to the behavior of such alteration-sensitive species as K2O, H2O-, CO2, S, Tl, and the iron oxidation ratio, the alteration is oxidative in the upper part and nonoxidative or even reducing in the lower part. The oxidative alteration may have resulted from low temperature basalt/seawater interaction, whereas hydrothermal solutions may be responsible for the nonoxidative alteration.

Raul Sciarretta y la epistemología del psicoanálisis en los años '70

Raúl Sciarretta formó, en sus grupos de estudio, a distintas generaciones de intelectuales del país. El testimonio de muchos psicólogos y psicoanalistas que asistieron a sus cursos -fundamentalmente a partir de la década del '70- impulsó el interroganteacerca de la participación e incidencia de este intelectual en la historia del 'campo psi' argentino. El presente trabajo pretende ser una contribución en ese sentido. Tendrá por objetivo analizar y contextualizar sus enseñanzas durante la década del '70, momento en el cual sus cursos estarán orientados al estudio del psicoanálisis a través de una aproximación epistemológica. De la sistematización de los datos recopilados en artículos y entrevistas pudo establecerse que la actividad de enseñanza de Sciarretta se desarrolló fundamentalmente en grupos de estudio privados a partir la década del '60 y hasta su muerte, en 1999. La temática especifica de sus cursos ira modificándose a lo largo de estos años, desde el abordaje de contenidos filosóficos en la década del '60- en el cual, entre otras cuestiones, se destacarán sobre todo sus cursos sobre 'El Capital' de Marx- hasta sus enseñanzas sobre psicoanálisis lacaniano que comienzan a fines de los '70 y continuarán durante la década del '80 y '90, dictando además, conferencias y seminarios sobre el tema, en Francia, España y Brasil. Entre estos dos momentos se sitúa el período de estudio abordado en el presente trabajo, sus cursos sobre 'epistemología del psicoanálisis' caracterizarán esta época. Su lectura epistemológica de la obra freudiana llegará a distintas partes del país influyendo, de este modo, en la formación de una gran cantidad de psicólogos y psicoanalistas. Tal es así que, para principios de la década del '70, esta lectura de Freud, no solo será trabajada al interior de sus grupos de estudio en Buenos Aires, sino que además será abordada en cursos específicos que dictará en diferentes lugares, como Rosario, Córdoba y Tucumán. Esta extensión de sus enseñanzas estará íntimamente vinculada al momento que atravesaba el psicoanálisis a nivel local, particularmente a la crisis de las categorías teóricas, institucionales y políticas que habían sostenido las condiciones de difusión y desarrollo del psicoanálisis hasta el momento. De hecho Sciarretta participó del movimiento que llevaría a la ruptura de la APA, y sus enseñanzas no serán ajenas a ese cuestionamiento. Es así que, a partir de la recopilación y análisis de datos relativos a este momento de su enseñanza y del estudio de las desgrabaciones mecanografiadas de sus clases dictadas en Buenos Aires entre 1970 y 1971, se pudieron reconstruir los objetivos, la significación y los efectos que producirá su 'epistemología del psicoanálisis' y que serán desarrollados en el presente trabajo. Se verá que este contexto Sciarretta realizaba una lectura epistemológica de la obra freudiana desde Bachelard, Althusser y Marx, que ponía en cuestión el psicoanálisis de la época y, fiel a su estilo, abría la posibilidad de una lectura constructiva, que permitiera producir a partir de lo leído. Así mismo ya en estos cursos comenzaba a trabajar las enseñanzas de Lacan vía Althusser, anticipando, por un lado, el rumbo que tomarán sus cursos en los años siguientes, pero fundamentalmente introduciendo, ya para esta época, a muchos psicoanalistas en la teoría lacaniana que algunos años después será preponderante en nuestro país