Contrǒle des concentrations d'aluminium dissous dans les eaux des sources thermales

We analized about 100 hot springs of different regions in France for dissolved Al. In an area where the chemical composition of the springs for major elements is about the same and the emergence temperatures are different, we usually observe correlations between dissolved Al and temperature. This correlation is positive in the case of high pH hot springs (Pyrénées). On the contrary, the correlation is negative for the CO₂ rich waters of the Massif Central (Vichy). We also observe intermediate patterns, where Al concentrations are roughly independant of the temperature.Using a set of consistant values of thermodynamical data for ions and minerals of Al, we find that the observed correlations between Al and temperature are related to the solubility of a mineral which is generally kaolinite.     

Glass-bearing gabbro inclusions in hyaloclastites from Tindfjallajökull,Iceland

Gabbro inclusions from Tindfjallajökull are divided into two types: I. Panidiomorphic gabbros of non-cumulative origin composed of plagioclase + olivine ± clinopyroxene and interstitil vesicular glass. They have formed in equilibrium with the host magma and may either represent a marginal facies or a highly solidified magma body. In the latter case the host magma or part of it could be mobilized interstitial liquid. II. Allotriomorphic-hypidiomorphic tholeiitic olivine gabbro and diorite xenoliths with scarce Ti-pargasite which have undergone less than 10% partial melting in the host magma forming melts of alkali basaltic or Hekla andesite-like compositions dependent on the original mineral assemblage. Such liquids, enriched in K₂O and possibly other incompatible elements, may contaminate basaltic magmas rising slowly through a gabbroic lower crust. Large scale production of andesites by partial melting of such rocks is not possible but would need more hydrous or differentiated source rocks.     

Geologic implications and potential hazards of scour depressions on bering shelf,Alaska

Flat-bottomed depression 50–150 m in diameter and 60–80 cm deep occur in the floor of Norton Sound, Bering Sea. These large erosional bedforms and associated current ripples are found in areas where sediment grain size is 0.063–0.044 mm (4–4.5 φ), speeds of bottom currents are greatest (20–30 cm/s mean speeds under nonstorm conditions, 70 cm/s during typical storms), circulation of water is constricted by major topographic shoals (kilometers in scale), and small-scale topographic disruptions, such as ice gouges, occur locally on slopes of shoals. These local obstructions on shoals appear to disrupt currents, causing separation of flow and generating eddies that produce large-scale scour. Offshore artificial structures also may disrupt bottom currents in these same areas and have the potential to generate turbulence and induce extensive scour in the area of disrupted flow. The size and character of natural scour depressions in areas of ice gouging suggest that large-scale regions of scour may develop from enlargement of local scour sites around pilings, platforms, or pipelines. Consequently, loss of substrate support for pipelines and gravity structures is possible during frequent autumn storms.     

The potential source of lead in the Permian Kupferschiefer bed of Europe and some selected Paleozoic mineral deposits in the Federal Republic of Germany

New lead isotopic compositions have been measured for Paleozoic bedded and vein ore deposits of Europe by the high precision thermal emission (triple filament) technique. Eleven samples have been analyzed from the Upper Permian Kupferschiefer bed with representatives from Poland to England, three samples from the Middle Devonian Rammelsberg deposit and one from the Middle Devonian Meggen deposit, both of which are conformable ore lenses and are in the Federal Republic of Germany (FRG); and also two vein deposits from the FRG were analyzed, from Ramsbeck in Devonian host rocks and from Grund in Carboniferous host rocks. For Kupferschiefer bed samples from Germany, the mineralization is of variable lead isotopic composition and appears to have been derived about 250 m.y. ago from 1700 m.y. old sources, or detritus of this age, in Paleozoic sedimentary rocks. Samples from England, Holland, and Poland have different isotopic characteristics from the German samples, indicative of significantly different source material (perhaps older). The isotopic variability of the samples from the Kupferschiefer bed in Germany probably favors the lead containing waters coming from shoreward (where poor mixing is to be expected) rather than basinward (where better mixing is likely) directions. The data thus support the interpretation of the metal source already given by Wedepohl in 1964. Data on samples from Rammelsberg and Meggen tend to be slightly less radiogenic than for the Kupferschiefer, about the amount expected if the leads were all derived from the same source material but 100 to 150 m.y. apart in time. The vein galena from Ramsbeck is similar to that from Rammelsberg conformable ore lenses, both in rocks of Devonian age; vein galena from Grund in Upper Carboniferous country rocks is similar to some bedded Kupferschiefer mineralization in Permian rocks, as if the lead composition was formed at about the same time and from similar source material as the bedded deposits. Although heat has played a more significant role in the formation of some of these deposits (veins and Rammelsberg-Meggen) than in others (Kupferschiefer), there is no indication of radically different sources for the lead, all apparently coming from sedimentary source material containing Precambrian detritus. One feldspar lead sample from the Brocken-Oker Granite is not the same in isotopic composition as any of the ores analyzed.Publication authorized by the Director, U.S. Geological Survey     

Zur Herkunft des Quarzzements. Abschätzung der Quarzauflösung in Silt- und Sandsteinen

The origin of quartz cement in sandstones can be attributed to supplies (1) from the surrounding shales, and (2) to a lower degree from dissolution of quartz on stylolites within the sandstones. A supply from the surrounding shales, which has been shown by the porosity decrease near the upper and lower surfaces of different sandstones (Füchtbauer, 1974), can be explained by the following observations in Upper Triassic and Middle Jurassic sandstones and siltstones of Northern Germany as well as in concretions of Devonian to Upper Cretaceous age from different localities:

1. Quartz grains in silt layers are flattened by dissolution compared with quartz grains of the same size in the adjacent sandstones, the amount of shrinking being about 35 percent (fig. 1).
2. Concretions prevent the enclosed insoluble residues from diagenesis. The main difference between the concretions and the adjacent shale of 31 occurrences examined is the quartz content, which is by 10–50 percent lower in the adjacent shale, due to diagenetical dissolution (fig. 2).

It is suggested that the dissolved silica was brought to the sandstones by the compaction stream of interstitial water percolating through the rock sequence, and that the sandstones acted as sinks triggering the dissolution. Only a small amount of silica, about 10 percent of the silica from dissolved quartz, is provided by the transition montmorillonite — illite. Both sources together would be able to explain the precipitation of 20 percent quartz cement in a sequence composed of 1/3 sandstones and 2/3 shales. In the sandstones mentioned above stylolites can be observed (fig. 3), the amplitudes of which increase from 0,5–1 mm to 2–5 mm with increasing depth, between 1300 and 2600 metres. The real amount of dissolution on each stylolite — about 4 mm — has been calculated using large mica which were collected by the stylolites from the adjacent sandstone. Using this figure, the decrease of porosity in the sandstones shown in fig. 4 can be quantitatively explained by the frequency of stylolite intercalations. It is suggested that this process, which was due to local diffusion, occurred late in diagenesis, when the compaction stream was already insufficient to move large quantities of silica.     

Boccardia hamata (Polychaeta:spionidae): A potential pest of the American oyster in the James River,Virginia

During a comprehensive survey of fauna associated with James River oyster reefs in 1971–72, a large population of the spionid polychaeteBoccardia hamata was found. The abundance of this boring species was greater than that of the well-known oyster pestPolydora websteri. B. hamata has not been reported previously in the Chesapeake Bay system and its occurrence on the east coast of the United States is not common. The large numbers in 1971–72 and continued presence ofB. hamata in 1975 suggests that the species may be well established in the James River. This may have some implications to the oyster industry if the species is as harmful as other boring spionids.     

Acquisition des ions alcalino-terreux par les eaux thermales carbogazeuses

Nous présentons différents arguments tendantàmontrer qu'une proportion importante deséléments alcalinoterreux présents dans les sources thermominérales du Massif Central français est acquise en subsurface lors de la remontée de l'eau. Au cours de ces réactions subsuperficielles, le rapport Na/K est peu modifié. Les hautes teneurs en Ca²⁺ et Mg²⁺ de ces eaux ne constituent pas un argument suffisant pour rejeter l'information fournie par le géothermomètre Na/K.Nous montronségalement que l'utilisation des rapports isotopiques du strontium comme indicateur d'origine doite?tre menée avec précautions.     

Diffusion of hydrogen through platinum membranes at high pressures and temperatures

The diffusion of hydrogen through platinum membranes has been measured at 450, 500, 550 and 600°C at 2000 bar pressure, using the hydrogen sensor technique. Ag + AgCl + 3 M HC1 was the starting solution inside the platinum tube. Hydrogen diffuses out of the platinum tube into a system containing Fe₂O₃ + Fe₃O₄ + H₂O; that is, a solution with a fixed hydrogen fugacity. After quench, the drop in f_H2 inside the platinum tube was calculated from measurements of pH and chloride molality. f_H2 is initially roughly proportional to $\text{t}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$. Diffusion constants were calculated from these data by numerical integration, and the results can be expressed by logD (cm²/sec) = ? 5489.6/T, K - 4.648.