Pressure-temperature and evolution of fluid compositions of Al2SiO5-bearing rocks,Mica Creek,B.C., in light of fluid inclusion data and mineral equilibria

Metamorphosed pelitic rocks from Mica Creek, British Columbia contain sillimanite, kyanite with minor fibrolite and andalusite-bearing quartz pods. Mineral equilibria were used to infer peak P-T conditions and fluid compositions in equilibrium with the solid phases. Fluid inclusions in three schist samples appear to be good indicators of conditions affecting those rocks during and after peak metamorphic conditions. In samples from two localities, fluid inclusions from schist and quartz-rich segregations have densities appropriate to the peak metamorphic conditions. The observed compositions for these fluids (low salinity with 12 mole % dissolved CO₂) agree with calculated values of 0.84 to 0.85, based upon paragonite-quartz-albite-Al₂SiO₅ equilibria. The fluids unmixed as the schists were uplifted and cooled; fluid inclusions trapped during this stage outline a solvus in the CO₂-H₂O-NaCl system. A later influx of fluids containing CH₄ and N₂ accompanied formation of andalusite-bearing plagioclaserich segregations. The restricted association of andalusite-bearing pods and low density fluids suggest a localized but pervasive fluid influx during uplift. Preservation of high density fluid inclusions during uplift and erosion, coupled with evidence for unmixing of H₂O- and CO₂-rich fluids on the solvus, provide constraints on the P-T uplift path.     

Contrasting geochemical signatures on land from the Middle and Late Permian extinction events

The end of the Palaeozoic is marked by two mass‐extinction events during the Middle Permian (Capitanian) and the Late Permian (Changhsingian). Given similarities between the two events in geochemical signatures, such as large magnitude negative δ¹³C anomalies, sedimentological signatures such as claystone breccias, and the approximate contemporaneous emplacement of large igneous provinces, many authors have sought a common causal mechanism. Here, a new high‐resolution continental record of the Capitanian event from Portal Mountain, Antarctica, is compared with previously published Changhsingian records of geochemical signatures of weathering intensity and palaeoclimatic change. Geochemical means of discriminating sedimentary provenance (Ti/Al, U/Th and La/Ce ratios) all indicate a common provenance for the Portal Mountain sediments and associated palaeosols, so changes spanning the Capitanian extinction represent changes in weathering intensity rather than sediment source. Proxies for weathering intensity chemical index of alteration, ?W and rare earth element accumulation all decline across the Capitanian extinction event at Portal Mountain, which is in contrast to the increased weathering recorded globally at the Late Permian extinction. Furthermore, palaeoclimatic proxies are consistent with unchanging or cooler climatic conditions throughout the Capitanian event, which contrasts with Changhsingian records that all indicate a significant syn‐extinction and post‐extinction series of greenhouse warming events. Although both the Capitanian and Changhsingian event records indicate significant redox shifts, palaeosol geochemistry of the Changhsingian event indicates more reducing conditions, whereas the new Capitanian record of reduced trace metal abundances (Cr, Cu, Ni and Ce) indicates more oxidizing conditions. Taken together, the differences in weathering intensity, redox and the lack of evidence for significant climatic change in the new record suggest that the Capitanian mass extinction was not triggered by dyke injection of coal‐beds, as in the Changhsingian extinction, and may instead have been triggered directly by the Emeishan large igneous province or by the interaction of Emeishan basalts with platform carbonates.     

Source(s) and cycling of the nonhydrolyzable organic fraction of oceanic particles

A major fraction of particulate organic carbon (POC) in the deep ocean remains molecularly uncharacterized. In an effort to determine the chemical characteristics and source(s) of sinking POC, we studied a nonhydrolyzable fraction of sinking POC using ¹³C NMR (nuclear magnetic resonance) spectroscopy and analytical pyrolysis. ¹³C NMR spectra and products from analytical pyrolysis of the nonhydrolyzable fraction exhibit a strongly aliphatic character that is distinct from that of bulk POC. The aliphatic nature of this fraction is consistent with its low stable carbon isotope values. We hypothesize that the nonhydrolyzable fraction derives to a significant extent from a refractory component of organisms that selectively accumulates, resulting in its manifestation as a major part of POC sinking to the deep ocean and in underlying sediments.     

Couplage des équations de transfert de masse et des lois d''interactions solution-solide par l''utilisation des lanthanides comme traceurs — Approche expérimentale

In underground flow tracing studies, the estimation of the nature and the importance of interactions undergone by the substance used very often constitutes an obstacle to good modeling of mass-transfer processes in solution.

We propose a method to quantify these phenomena by the use of lanthanides as tracers.

For this study, we set up an analytical methodology adapted to routine measurements. The quality of five lanthanides as indicators has been examined. We have demonstrated the formation, by substitution, of a carbonate complex which is extremely stable in the natural environment. The field experiments carried out demonstrated the efficiency of those tracers and confirmed their great stability.

Tracer recovery graphs show that, in accord with our hypothesis, convection and dispersion are identical for all the lanthanide elements. Moreover, we have established a direct relation between their fixing rate on earth materials and the value of their stability constants.

Thus, we demonstrate the possibility of correlative multitracing, with known and quantifiable interelement relations.

Résumé

Dans les études de circulations souterraines par traceur, l'estimation de la nature et de l'importance des interactions subies par la substance utilisée constitue, bien souvent, un obstacle à une bonne modélisation des processus de transfert de masse en solution.

Nous proposons une méthode de quantification de ces phénomènes par l'utilisation des lanthanides comme traceurs.

Pour cette étude, nous avons mis au point une méthodologie analytique adaptée aux mesures de routine. Les qualités, en tant qu'indicateurs, de cinq lanthanides ont été examinées. Nous avons démontré la formation, par substitution, d'un complexe carbonaté extrèment stable en milieu naturel. Les expériences de terrain réalisées ont prouvé l'efficacité de ces traceurs et confirmé leur grande stabilité.

Les courbes de restitution obtenues ont montré que, conformément à nos hypothèses, la convection et la dispersion sont identiques pour l'ensemble de ces éléments. De plus, il a été établi une relation directe entre leurs taux de fixation sur le terrain et la valeur de leurs constantes de stabilité.

On dispose ainsi d'une possibilité de multitraçage corrélatif, avec des relations interélémentaires connues et quantifiables.     

A review of applications of microwave radiometry to oceanography

The thermal microwave radiation from the ocean surface as seen from space is a function of the surface temperature and wind speed and is modified by liquid water and water vapor in the intervening atmosphere. Further, if the ocean surface is frozen, the emissivity is drastically increased and the effect of the intervening atmosphere is generally negligible. The emissivity of first-year ice is somewhat larger than that of multi-year ice.The data from the Electrically Scanning Microwave Radiometers (ESMR's) on the Nimbus-5 and —6 satellites operating at wavelengths of 1.55 cm and 8 mm, respectively, can be interpreted in terms of rain rate, ice coverage and first-year versus multi-year ice determination. The rain-rate data are being used to establish a climatology of rainfall over the oceans. The ice data are being used by the United States Navy in support of international scientific efforts in the Antactic region. Both ice and rain data sets have been generated for the Global Atmospheric Research Project Data Systems Test.It is possible, by making multifrequency measurements, to separate the surface and atmospheric effects and to make useful measurements of sea surface temperature, surface wind speed, and atmospheric parameters along with improved measurements of rain and ice.     

Seismic observations at an overstep of the western North Anatolian Fault (Abant–Sapanca region, Turkey)

The course of the active North Anatolian Fault system from Lake Abant to Lake Sapanca was traced by its high micro-earthquake activity. If approaching from the east this section includes a broad south to north overstep (fault offset) of the main fault. Local seismicity has been recorded in this area by a semi-permanent network of 8 stations since 1985 within the frame of the Turkish–German Joint Project for Earthquake Research. The effect of the overstep and its complex fracture kinematics are reflected by the seismicity distribution, the variations of composite fault-plane solutions, and by the spatial coda-Q distribution. Areas of different stress orientation can be distinguished and assigned to different groups of faults. The stresses and the tectonic pattern only in part correspond to a simple model of an extensional overstep and its correlative pull-apart basin. Other types of deformation involved are characterized by normal faulting on faults parallel to the general course of the main strike-slip fault and by synthetic strike-slip faults oriented similar to Riedel shears. Shear deformation by this fault group widely distributed in an area north and east of the main fault line may play an important role in the evolution of the overstep. The development of a pull-apart basin is inhibited along the eastern half of the overstep and compatibility of both strands of the main fault (Bolu–Lake Abant and Lake Sapanca– Izmit–Marmara Sea) seems to be achieved with the aid of the fault systems mentioned. The extension of the missing part of the pull-apart basin seems to be displaced to positions remote from the Lake Abant–Lake Sapanca main fault line, i.e. to the Akyaz?–Düzce basin tract. Highest Q-values (lowest attenuation of seismic waves) were found in the zone of highest seismicity north and west of the overstep which is the zone of strongest horizontal tension. If high coda-Q is an indicator for strong scattering of seismic waves it might be related to extensional opening of fractures.     

Seismic model of the lithosphere of the East European Platform beneath the Baltic Sea-Black Sea profile

This paper presents the results of seismic measurements along the Baltic Sea-Black Sea profile. The basic wave groups recorded up to distances of 900 km are characterized. The main elements of a lithospheric model of the southwestern part of the Precambrian East European Platform are given. The thickness of the Earth's crust is about 45 km and the mean velocity of the crust is about 6.3 km/s. At a depth of 65 km, the velocity increases from 8.2 to 8.5 km/s. In the depth interval 110 to 135 km, there is a series of layers with low and high velocities. The lower boundary of the lithosphere is probably defined by the boundary at a depth of 110 km.     

P travel-times from Nevada Test Site explosions and the determination of average global P travel-times

An analysis of P travel-times from the Nevada Test Site is carried out using data from 23 explosions between 1966 and 1976. Results show a scatter of travel times which may partly arise in the lower mantle. P travel-times over the distance range 25–100° are 2.0–2.5 s faster than the Jeffreys-Bullen travel times.     

Effects of the oophagous bivalve Acesta oophaga on the morphology and fecundity of its deep‐sea tubeworm host,Lamellibrachia luymesi

The deep‐sea bivalve Acesta oophaga lives attached to the anterior end of the vestimentiferan tubeworm, Lamellibrachia luymesi, at cold methane seeps. The bivalve is found almost exclusively on female tubeworms, where it consumes the lipid‐rich eggs of L. luymesi that are spawned year round (Biological Bulletin, 209, 2005, 87). It is apparent that A. oophaga benefits directly from this close association, but the consequences for the tubeworm host may be more complicated than just a simple predator–prey interaction. Since A. oophaga completely surrounds the tube opening and plume of the worm, it is likely that its presence would limit oxygen uptake by L. luymesi, thereby inhibiting worm growth and reproduction. We hypothesized that occupied tubeworms would compensate for this by growing larger plumes for oxygen uptake. To explore the effects of bivalve presence/absence on female tubeworms, several morphological features, including body size, plume length, tube diameter, and tube segment length, as well as instantaneous fecundity, were compared. Results suggest that the mere presence of A. oophaga has a significant impact on the morphology of its host worm, as all measures of worm size, except for tube segment length, were significantly greater with clams present. Additionally, instantaneous fecundity was 3.5 times higher in occupied worms, implying that tubeworms are not oxygen‐deprived or energy limited as a result of bivalve presence. Our findings suggest that the association between these two deep‐sea organisms may be a more complex form of symbiosis than the simple predator–prey relationship, as previously thought.