Microthermometry and Raman analysis of fluid inclusions in different generations of quartz veins of the Athabasca Basin

The Athabasca Basin (Canada) contains the highest grade unconformity-type uranium deposits in the world. Underlying the Athabasca Group sedimentary rocks of the Dufferin Lake zone are variably graphitic pelitic schists (VGPS), altered to chlorite and hematite (Red/Green Zone: RGZ), and locally bleached near the unconformity during paleoweathering and/or later fluid interaction, leading to a loss of graphite near the unconformity. Fluid inclusions were examined in different generations of quartz veins, using microthermometry and Raman analysis, to characterize and compare the different fluids that interacted with the RGZ and the VGPS. In the VGPS, CH4-, N2- and CO2-rich fluids circulated. CH4- and N2-rich fluids could be the result of the breakdown of graphite to CH4/CO2, whereas N2-rich fluid is interpreted to be the result of breakdown of feldspars/micas to NH4+/N2. In the RGZ, highly saline fluids interpreted to be basinally derived have been recorded. The circulation of the two types of fluids (carbonic and brines) occurred at two different distinct events: 1) during the retrograde metamorphism of the basement rocks before the deposition of the Athabasca Basin for the carbonic fluids, and 2) after the deposition of the Athabasca Basin for the brines. Thus, in addition to possibly be related to graphite depletion in the RGZ, the brines can be linked to uranium mineralization.

Carlos Marzal : Poesía de la experiencia y poesía del pensamiento

Me propongo examinar aquí de qué modo comienzan a reformularse los presupuestos de la llamada "poesía de la experiencia" española en la escritura de los años 90. Aspiración a la legibilidad, riguroso cuidado formal, búsqueda de complicidad con el lector a partir de un poema hecho con trazos de emoción y fragmentos de vida parecen ser los mismos pilares que sustentan toda la poesía experiencial, pero en algunas escrituras de los años 90 como la de Carlos Marzal, por ejemplo, se le imprime un giro más y un cambio de tono. Se trata de poemas reflexivos (y autorreflexivos) que indagan simultáneamente en la intimidad del sujeto poético (el planteo de la intimidad amorosa pero también -y con no menor peso- las problemáticas de corte filosófico existencial) desde los supuestos de lo que podríamos denominar "poesía de pensamiento" y lo hace ostentando una genealogía poética que lo vincula con Jaime Gil de Biedma y Francisco Brines, entre sus principales referentes

Strontium isotopic ratios of evaporites of the Tyrrhenian Sea

Strontium isotopic ratios of gypsums recovered from upper Miocene (Messinian) evaporites at ODP Leg 107 Holes 652A, 653B, and 654A (Tyrrhenian Sea) are lower than expected. The values for the Messinian balatino-like gypsum, single gypsum crystals, and anhydrites range from 0.70861 to 0.70886 and are approximately 25 * 10**-5 less than would be expected for evaporites precipitated from Messinian seawater (0.70891-0.70902). Pre-evaporitic planktonic foraminifers from Hole 654A show variable degrees of dolomitization and 87Sr/86Sr values that irregularly decrease upward from normal marine values approximately 81m below the lowest evaporite occurrence. This suggests diagenetic alteration by advecting interstitial water with a low 87Sr/86Sr ratio or that the lower Sr isotopic ratios for the Messinian evaporites could have resulted from a greater influence of fresh water on the Sr isotopic composition of the desiccating Tyrrhenian Sea. Fluctuations of the 87Sr/86Sr-ratio for evaporites in the sedimentary cycles recognized for Holes 653B and 654A, the generally low Sr isotopic ratio of river water entering the Mediterranean Sea, and the presence of dwarf marine microfossils suggest that the 87Sr/86Sr ratio of the evaporites responded to hydrologic variations in a very restricted basin with variable rates of marine and fresh water input. The strontium isotopic ratios of the Messinian anhydrites from the proposed lacustrine sequence at Hole 652A fall in the same range as the marine evaporites from Holes 654A and 653B. This suggests a common or similar origin of the brines at the three locations. The complex depositional and hydrologic conditions in the Mediterranean during the Messinian salinity crisis preclude the use of Sr isotopic values from the evaporites for stratigraphic correlation and dating. They are, however, very useful in the interpretation of the depositional history of the basin. General calculations assuming a closed system suggest that the 87Sr/86Sr ratio of Messinian seawater (-0.7090) could be reduced to that of the evaporites (-0.7087) by mixing with fresh water (e.g., Nile River) in times of 10**4 to 10**5 yr.

La otra revolución : Debates del medio siglo español

Este trabajo se propone espigar las condiciones del funcionamiento en el campo intelectual español del medio siglo de un grupo de poetas, los denominados integrantes de la "promoción del 50", que, con diversos perfiles, inauguran la "otra revolución" , a la vez en continuidad y disenso con la promovida por los poetas sociales fundadores de la generación precedente. En este sentido, los autores que integran inicialmente el grupo -entre los que destacamos a Jaime Gil de Biedma, José Angel Valente, Angel González, Francisco Brines, José Agustín Goytisolo, Claudio Rodríguez, Carlos Barral- , se reafirman provocativamente, por los años de constitución del grupo y, algunos de ellos, más allá de este período, merced a una serie de polémicas que conmocionan, hacia delante y hacia atrás, la serie literaria española, con propuestas que exceden el mero utillaje temático o conceptual: poesía como comunicación -poesía como conocimiento, mímesis y lenguaje, las figuraciones del sujeto de la escritura y su condición ficcional, el diálogo con voces foráneas y una fecunda revisitación de las siempre presentes enseñanzas machadianas.

Stable isotope ratios and foraminiferal abundance of sediment cores from the Western Iberian Margin

Rapid climate changes at the onset of the last deglaciation and during Heinrich Event H4 were studied in detail at IMAGES cores MD95-2039 and MD95-2040 from the Western Iberian margin. A major reorganisation of surface water hydrography, benthic foraminiferal community structure, and deepwater isotopic composition commenced already 540 years before the Last Isotopic Maximum (LIM) at 17.43 cal. ka and within 670 years affected all environments. Changes were initiated by meltwater spill in the Nordic Seas and northern North Atlantic that commenced 100 years before concomitant changes were felt off western Iberia. Benthic foraminiferal associations record the drawdown of deepwater oxygenation during meltwater and subsequent Heinrich Events H1 and H4 with a bloom of dysoxic species. At a water depth of 3380 m, benthic oxygen isotopes depict the influence of brines from sea ice formation during ice-rafting pulses and meltwater spill. The brines conceivably were a source of ventilation and provided oxygen to the deeper water masses. Some if not most of the lower deep water came from the South Atlantic. Benthic foraminiferal assemblages display a multi-centennial, approximately 300-year periodicity of oxygen supply at 2470-m water depth. This pattern suggests a probable influence of atmospheric oscillations on the thermohaline convection with frequencies similar to Holocene climate variations. For Heinrich Events H1 and H4, response times of surface water properties off western Iberia to meltwater injection to the Nordic Seas were extremely short, in the range of a few decades only. The ensuing reduction of deepwater ventilation commenced within 500-600 years after the first onset of meltwater spill. These fast temporal responses lend credence to numerical simulations that indicate ocean-climate responses on similar and even faster time scales.

Barium in seawater and sediments from the Artic Ocean

As part of ongoing circulation studies in the Arctic, seawater samples for dissolved Ba concentrations were obtained during Sep.-Oct., 1992 at several locations in the Bering Strait, Eastern Chukchi and Southern Beaufort Seas. The results reveal a dynamic rang (10 to 150 nmol/kg) for this element in the Arctic equal to or greater than that in combined Atlantic, Indian and Pacific oceans. Lowest levels are observed in surface waters, with values tending to decrease northwards in the direction of currents generally flowing frorn the Bering Strait along the Alaskan coast. Low surfacc concentrations tend to be accompanied by relatively enriched near bottom levels. On the basis of these spatial distributions, hydrographic observations and a knowledge of its behavior in other marine settings, it appears that Ba can be significantly depleted from surface waters as a result of the highly seasonal biological aclivities over Arctic marginal shelves. Removal at the surface is counteracted to some extent by regeneration at depth or in the sediments and by riverine inputs. The biologically related drawdown is likely to enhance the contrast between 'background' surface Ba levels in the Arctic and waters imprinted by regeneration and/or rivers, These preliminary findings suggest that Ba holds particular promise for tracing river waters and the ventilation of halodine waters hy laterally sinking brines produced during ice formation over the shelves.

Carlos Marzal : Poesía de la experiencia y poesía del pensamiento

Me propongo examinar aquí de qué modo comienzan a reformularse los presupuestos de la llamada "poesía de la experiencia" española en la escritura de los años 90. Aspiración a la legibilidad, riguroso cuidado formal, búsqueda de complicidad con el lector a partir de un poema hecho con trazos de emoción y fragmentos de vida parecen ser los mismos pilares que sustentan toda la poesía experiencial, pero en algunas escrituras de los años 90 como la de Carlos Marzal, por ejemplo, se le imprime un giro más y un cambio de tono. Se trata de poemas reflexivos (y autorreflexivos) que indagan simultáneamente en la intimidad del sujeto poético (el planteo de la intimidad amorosa pero también -y con no menor peso- las problemáticas de corte filosófico existencial) desde los supuestos de lo que podríamos denominar "poesía de pensamiento" y lo hace ostentando una genealogía poética que lo vincula con Jaime Gil de Biedma y Francisco Brines, entre sus principales referentes

La otra revolución : Debates del medio siglo español

Este trabajo se propone espigar las condiciones del funcionamiento en el campo intelectual español del medio siglo de un grupo de poetas, los denominados integrantes de la "promoción del 50", que, con diversos perfiles, inauguran la "otra revolución" , a la vez en continuidad y disenso con la promovida por los poetas sociales fundadores de la generación precedente. En este sentido, los autores que integran inicialmente el grupo -entre los que destacamos a Jaime Gil de Biedma, José Angel Valente, Angel González, Francisco Brines, José Agustín Goytisolo, Claudio Rodríguez, Carlos Barral- , se reafirman provocativamente, por los años de constitución del grupo y, algunos de ellos, más allá de este período, merced a una serie de polémicas que conmocionan, hacia delante y hacia atrás, la serie literaria española, con propuestas que exceden el mero utillaje temático o conceptual: poesía como comunicación -poesía como conocimiento, mímesis y lenguaje, las figuraciones del sujeto de la escritura y su condición ficcional, el diálogo con voces foráneas y una fecunda revisitación de las siempre presentes enseñanzas machadianas.

La otra revolución : Debates del medio siglo español

Este trabajo se propone espigar las condiciones del funcionamiento en el campo intelectual español del medio siglo de un grupo de poetas, los denominados integrantes de la "promoción del 50", que, con diversos perfiles, inauguran la "otra revolución" , a la vez en continuidad y disenso con la promovida por los poetas sociales fundadores de la generación precedente. En este sentido, los autores que integran inicialmente el grupo -entre los que destacamos a Jaime Gil de Biedma, José Angel Valente, Angel González, Francisco Brines, José Agustín Goytisolo, Claudio Rodríguez, Carlos Barral- , se reafirman provocativamente, por los años de constitución del grupo y, algunos de ellos, más allá de este período, merced a una serie de polémicas que conmocionan, hacia delante y hacia atrás, la serie literaria española, con propuestas que exceden el mero utillaje temático o conceptual: poesía como comunicación -poesía como conocimiento, mímesis y lenguaje, las figuraciones del sujeto de la escritura y su condición ficcional, el diálogo con voces foráneas y una fecunda revisitación de las siempre presentes enseñanzas machadianas.

Carlos Marzal : Poesía de la experiencia y poesía del pensamiento

Me propongo examinar aquí de qué modo comienzan a reformularse los presupuestos de la llamada "poesía de la experiencia" española en la escritura de los años 90. Aspiración a la legibilidad, riguroso cuidado formal, búsqueda de complicidad con el lector a partir de un poema hecho con trazos de emoción y fragmentos de vida parecen ser los mismos pilares que sustentan toda la poesía experiencial, pero en algunas escrituras de los años 90 como la de Carlos Marzal, por ejemplo, se le imprime un giro más y un cambio de tono. Se trata de poemas reflexivos (y autorreflexivos) que indagan simultáneamente en la intimidad del sujeto poético (el planteo de la intimidad amorosa pero también -y con no menor peso- las problemáticas de corte filosófico existencial) desde los supuestos de lo que podríamos denominar "poesía de pensamiento" y lo hace ostentando una genealogía poética que lo vincula con Jaime Gil de Biedma y Francisco Brines, entre sus principales referentes

Results of analyses of fluid inclusions from ODP Site 735B, Leg 118 and 176

Microthermometric and isotopic analyses of fluid inclusions in primitive olivine gabbros, oxide gabbros, and evolved granitic material recovered from Ocean Drilling Program Hole 735B at the Southwest Indian Ridge provide new insights into the evolution of C-O-H-NaCl fluids in the plutonic foundation of the oceanic crust. The variably altered and deformed plutonic rocks span a crustal section of over 1500 m and record a remarkably complex magma-hydrothermal history. Magmatic fluids within this suite followed two chemically distinct paths during cooling through the subsolidus regime: the first path included formation of CO2+CH4+H2O+C fluids with up to 43 mole% CH4; the second path produced hypersaline brines that contain up to 50% NaCl equivalent salinities. Subsequent to devolatilization, respeciation of magmatic CO2, attendant graphite precipitation, and cooling from 800°C to 500°C promoted formation of CH4-enriched fluids. These fluids are characterized by average d13C(CH4) values of -27.1+/-4.3 per mil (N=45) with associated d13C(CO2) compositions ranging from -24.9 per mil to -1.9 per mil (N=39), and average dD values of exsolved vapor of -41+/-12 per mil (N=23). In pods, veins, and lenses of highly fractionated residual material, hypersaline brines formed during condensation and by direct exsolution in the absence of a conjugate vapor phase. Entrapped CO2+CH4+H2O-rich fluids within many oxide-bearing rocks and felsic zones are significantly depleted in 13C (with d13C(CO2) values down to about -25 per mil) and contain CO2 concentrations higher than those predicted by equilibrium devolatilization models. We hypothesize that lower effective pressures in high-temperature shear zones promoted infiltration of highly fractionated melts and compositionally evolved volatiles into focused zones of deformation, significantly weakening the rock strength. In felsic-rich zones, volatile build-up may have driven hydraulic fracturing of gabbroic wall rocks resulting in the formation of magmatic breccias. Comparison of isotopic compositions of fluids in plutonic rocks from 735B, the MARK area of the Mid-Atlantic Ridge, and the Mid-Cayman Rise indicate (1) that the carbon isotope composition of the lower oceanic crust may be far more heterogeneous than previously believed and (2) that carbon-bearing species in the oceanic crust and their distribution at depth are highly variable.

Chemical composition of rocks and minerals from the Karymsky volcanic center, Eastern Kamchatka

The powerful eruption in the Akademii Nauk caldera on January 2, 1996 marked a new activity phase of the Karymsky volcano and became a noticeable event in the history of modern volcanism in Kamchatka. The paper reports data obtained by studying more than 200 glassy melt inclusions in phenocrysts of olivine (Fo82-72), plagioclase (An92-73), and clinopyroxene (Mg# 83-70) in basalts of the 1996 eruption. The data were used to estimate composition of the parental melt and physicochemical parameters of the magma evolution. According to our data, the parental melt corresponded to low magnesium, high aluminum basalt (SiO2 = 50.2%, MgO = 5.6%, Al2O3 = 17%) of the mildly potassium type (K2O = 0.56%) and contained much dissolved volatile components (H2O = 2.8%, S = 0.17%, and Cl = 0.11%). Melt inclusions in the minerals are similar in chemical composition, a fact testifying that the minerals crystallized simultaneously with one another. Their crystallization started at pressure ~1.5 kbar, proceeded within a narrow temperature range of 1040+/-20°C, and continued until near-surface pressure ~100 bar was reached. Degree of crystallization of the parental melt during its eruption was close to 55%. Massive crystallization was triggered by H2O degassing under pressure <1 kbar. Magma degassing in an open system resulted in escape of 82% H2O, 93% S, and 24% Cl (of their initial contents in the parental melt) to the fluid phase. Release of volatile compounds to the atmosphere during the eruption that lasted for 18 h was estimated as 1.7x10**6 t H2O, 1.4x10**5 t S, and 1.5x10**4 t Cl. Concentrations of most incompatible trace elements in the melt inclusions are close to those in the rocks and to the expected fractional differentiation trend. Melt inclusions in plagioclase were found to be selectively enriched in Li. The Li-enriched plagioclase with melt inclusions thought to originate from cumulate layers in the feeding system beneath Karymsky volcano, in which plagioclase interacted with Li-rich melts/brines and was subsequently entrapped and entrained by the magma during the 1996 eruption.

A coupled model for carbon and radiocarbon evolution during the last deglaciation, link to model results

Changes in the ventilation of the Southern Ocean are thought to play an important role on deglacial carbon and radiocarbon evolution, but have not been tested within a coupled climate-carbon model. Here, we present such a simulation based on a simple scenario of transient deglacial sinking of brines - sea-ice salt rejections - around Antarctica, which modulates Southern Ocean ventilation. This experiment is able to reproduce deglacial atmospheric changes in carbon and radiocarbon but also ocean radiocarbon records measured in the Atlantic, Southern and Pacific Oceans. Simulated for the first time in a fully coupled climate-carbon model including radiocarbon, our modeling results suggest that the deglacial changes in atmospheric carbon dioxide and radiocarbon were achieved by means of a breakdown in the glacial brine-induced stratification of the Southern Ocean.