Noble gas systematics of deep rift zone glasses from Loihi Seamount, Hawaii

We report new noble gas fusion and crushing data for six pillow rim glasses, recovered between 3 and 5 km water depth on the south rift zone of Loihi Seamount, Hawaii. Helium abundances of the glasses vary from 0.3 to 2.3 μcc/g, with ⁴He/³He ratios between 30000 and 27000 (24–27 R_A), similar to previously reported values. The neon data form a correlation line which is similar to the Loihi-Kilauea line reported by Honda et al. [1], but extends to much higher ratios, up to 12.9 and 0.0382 for the ²⁰Ne/²²Ne and ²¹Ne/²²Ne ratios, respectively. This provides conclusive evidence for the suggestion that the Hawaiian plume, thought to originate in the lower mantle, has a solar-like ²⁰Ne/²²Ne composition [1], but a slightly higher ²¹Ne/²²Ne ratio. ⁴⁰Ar/³⁶Ar ratios of the deep rift-zone glasses are as high as 2600, and show a positive correlation with neon isotopic ratios. In contrast to neon and argon, all xenon isotopic compositions are isotopically indistinguishable from air, which either suggests preferential atmospheric contamination of xenon, or could indicate an atmospheric xenon isotopic composition for the lower mantle.     

Typologie et mode de mise en place des roches magmatiques dans les Pyrénées hercyniennes

Résumé L'évolution géodynamique hercynienne des Pyrénées se caractérise par une importante activité magmatique à l'origine de corps plutomques de taille, de composition et de niveaux de mise en place différents. A partir de ces caractéristiques nous avons pu établir une typologie qui nous a permis de distinguer deux types principaux de massifs: 1) les massifs de composition homogène, acides (massifs de type HA) ou basiques (massifs de type HB), localisés dans les grands ensembles métamorphiques régionaux et 2) les massifs de composition hétérogène, formés par l'association de roches basiques et de roches acides dont la répartition spatiale a permis de distinguer les massifs de type CA (roches acides au coeur du massif), les massifs de type CB (roches basiques au coer du massif) et les massifs de type CR (récurrences de lentilles de roches basiques dans un massif zoné de type CA ou CB), mis en place dans le Paléozoïque supérieur généralement loin des grands ensembles métamorphiques. Tous ces massifs se sont mis en place diapiriquement au cours du métamorphisme régional et de la déformation hercynienne majeure.

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One of the main characteristics of the Hercynian geodynamic evolution of the Pyrenees is an intense magmatic activity producing large plutonic bodies. They have different sizes, various compositions and distinct emplacement levels. From these characteristics, a typology for these massifs is defined. Two main types of massifs have been recognized: 1) massifs with an homogenous composition founded in large regional metamorphic areas, and 2) massifs with an heterogenous composition of acid and basic rocks, whose spatial disposition permits the recognition of three sub-types: a) the CA type where acid rocks are at the core of the massif; b) the CB type where basic rocks are at the core of the massif, and c) the CR type where numerous basic xenoliths are scattered within either a CA or a CB type massif. These heterogenous massifs generally occur within Upper Paleozoic rocks and usually far away from regional metamorphic areas. All of these massifs were emplaced diapirically during the regional metamorphism and the main Hercynian deformation.

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Zusammenfassung Ein wichtiges charakteristisches Merkmal der geodynamischen Entwicklung der Pyrenäen während der herzynischen Phase ist eine hohe magmatische Aktivität, auf die Plutone größerer Ausdehnung zurückgeführt werden. Größe, Mineralogie und Erstarrungstiefe der Plutone variieren. Anhand dieser Charakteristika können die Intrusivkörper in zwei Hauptgruppen differenziert werden. Die erste Gruppe (1) sind Plutone homogener Zusammensetzung in regionalmetamorph überprägten Gebieten. Die zweite sind heterogen zusammengesetzte Plutone (2) saurer und basischer Magmatite, deren räumliche Anordnung eine Untergliederung in drei Untergruppen ermöglicht:a) Bei dem CA-Typ befinden sich saure Gesteine im Kern; bei b), dem CB-Typ, liegen basische Gesteine im Kern vor und bei c), einem CR genannten Typ, sind zahlreiche basische Xenolithe entweder in dem CA-oder dem CB-Typ verstreut vorhanden. Diese heterogenen Plutone findet man allein in spätpaläozoischen Gesteinen und in der Regel weit entfernt von Gebieten, die metamorph beeinflußt wurden. Sämtliche Plutone haben eine Diapir-ähnliche Form und intrudierten zeitgleich mit der Regionalmetamorphose und der Hauptphase der herzynischen Deformation.

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MELIMEX,an experimental heavy metal pollution study: Oligochaetes and chironomid larvae in heavy metal loaded and control limno-corrals

In two limno-corrals loaded with heavy metals the density of tubificid worms and chironomid larvae was higher than in the control. The better oxygen conditions observed in the heavy metal loaded corrals might explain this discrepancy. The higher oxygen concentration at the sediment-water interface was due to lower organic sedimentation, consequence of the primary production reduced by heavy metals. In all limno-corrals, the tubificid populations consisted ofTubifex tubifex. The size structure of tubificid populations in the heavy metal loaded corrals indicated a delayed reproduction compared to the control.     

Atmospheric response to the North Atlantic Ocean variability on seasonal to decadal time scales

The NCEP twentieth century reanalyis and a 500-year control simulation with the IPSL-CM5 climate model are used to assess the influence of ocean-atmosphere coupling in the North Atlantic region at seasonal to decadal time scales. At the seasonal scale, the air-sea interaction patterns are similar in the model and observations. In both, a statistically significant summer sea surface temperature (SST) anomaly with a horseshoe shape leads an atmospheric signal that resembles the North Atlantic Oscillation (NAO) during the winter. The air-sea interactions in the model thus seem realistic, although the amplitude of the atmospheric signal is half that observed, and it is detected throughout the cold season, while it is significant only in late fall and early winter in the observations. In both model and observations, the North Atlantic horseshoe SST anomaly pattern is in part generated by the spring and summer internal atmospheric variability. In the model, the influence of the ocean dynamics can be assessed and is found to contribute to the SST anomaly, in particular at the decadal scale. Indeed, the North Atlantic SST anomalies that follow an intensification of the Atlantic meridional overturning circulation (AMOC) by about 9 years, or an intensification of a clockwise intergyre gyre in the Atlantic Ocean by 6 years, resemble the horseshoe pattern, and are also similar to the model Atlantic Multidecadal Oscillation (AMO). As the AMOC is shown to have a significant impact on the winter NAO, most strongly when it leads by 9 years, the decadal interactions in the model are consistent with the seasonal analysis. In the observations, there is also a strong correlation between the AMO and the SST horseshoe pattern that influences the NAO. The analogy with the coupled model suggests that the natural variability of the AMOC and the gyre circulation might influence the climate of the North Atlantic region at the decadal scale.     

An improved index of environmental quality for Swiss rivers based on benthic invertebrates

A total of 1424 samples of benthic invertebrates, collected in 56 rivers of western Switzerland (canton of Vaud), was used to improve the RIVAUD (Rivers of Vaud) index of environmental quality. This index, described for the first time in 1989, was based on total number of taxa and on number of taxa intolerant of pollution (Plecoptera, Heptageniidae, and Trichoptera with a case). The 1995 version of RIVAUD, called RIVAUD 95, presented a larger range of values (0–20) than the previous one (0–10), to describe more precisely the variations of environmental quality. According to RIVAUD 95, the environmental quality of Swiss rivers increased with the altitude of sampling sites because anthropogenic impacts decreased along the same gradient. This altitudinal pattern was used to define classes of environmental quality which can be adapted to the rivers of other regions.     

The occurrence of lead in Antarctic recent snow,firn deposited over the last two centuries and prehistoric ice

Concentrations of lead have been measured by ultraclean Isotope Dilution Mass Spectrometry in snow cores covering the last two centuries collected at an inland site in East Antarctica using an ultra clean all plastic hand operated auger and in a prehistoric blue ice block collected at an Antarctic coastal site. Lead contamination of 16 to 200 pg Pb/g existed on the outside of the snow cores, but the measured concentrations decreased more or less abruptly along a radius from the outside to the centers of the snow cores, establishing interior values in the 1 to 5 pg Pb/g range. Some of these interior values are however possibly still slightly affected by lead contamination which could have intruded to the center of the cores because of slight melting of some of the snow cores before laboratory analysis. The interior of the blue ice block appears not to have been significantly contaminated, and contains about 1.7 pg Pb/g.These new data show that most previously published data on lead in Antarctic snow and ice were in high positive error because of contamination during field sampling, laboratory analysis or both. They show that lead concentrations could not have increased in Antarctic snows or ice from prehistoric times to present more than 2 to 3 fold, confirming that the remote polar areas of the Southern Hemisphere are still little affected by industrial lead pollution. Prehistoric Antarctic ice is shown to contain about 1 pg Pb/g natural excess lead above silicate dust lead; this excess cannot be entirely accounted for by volcanoes or sea spray, which suggests the possible existence of some other unknown natural source of prehistoric excess lead. Present day mean eolian fallout flux of lead in Antarctica is estimated to be about 0.07 ng Pb cm^?2 yr^?1, which stands in about the same proportion to that in the South Pacific Westerlies (about 1:30) as the flux in Greenland is observed to stand to those in the North Pacific and North Atlantic Westerlies.     

Conditions for the arrest of a vertical propagating dyke

Magma ascent towards the Earth’s surface occurs through dyke propagation in the vast majority of cases. We investigate two purely mechanical effects unrelated to cooling or solidification that lead to the arrest of propagation, so that no eruption occurs. The first is that the input of magma from the source is not maintained continuously, such that a fixed volume of magma is released. Laboratory experiments show that, in this case, the dyke stops at a finite distance from the source. This behaviour is specific to the fracturing process in 3-D. We derive a relationship for the minimum magma volume required for an eruption as a function of magma buoyancy and source depth. When large magma volumes are available, eruption may also be prevented by a thick low density layer in the upper crust. Numerical studies of dyke propagation show that the dyke continues to rise even though it is negatively buoyant. Magma accumulates in a swollen nose region at the interface between the low density layer and the dense basement. Magma overpressure is largest at this interface and increases with increasing penetration into the upper layer. It may become large enough to induce horizontal fractures in the dyke walls and lateral intrusion of a sill, which prevents eruption. This requires that the thickness of the low density layer exceeds a threshold value that depends on the density contrast between magma and host rock. If the magma volume is smaller than a threshold value, neither sill intrusion nor eruption are possible and magma gets stored in a horizontal blade-shaped dyke straddling the interface. Scaling laws for variations of ascent rate and for the minimum magma volume allow diagnosis of a failed eruption.     

Design and implementation of an image stabilization device at the THEMIS solar telescope

An image stabilizer has been inserted into the optical path of the THEMIS solar telescope. THEMIS is a Ritchey–Chretien reflector telescope using an altazimuthal mount and closely tied to its spectrograph. The optical and mechanical design, implementation and system tests are described, and emphasis is put on the complexity of situations that this stabilizer must accept, including the scanning of the solar surface while stabilizing. The current closed-loop crossover frequency of the device is 65 Hz at ??3 dB on all typical solar scenes.