The Caledonian deformed ordovician of the Rügen area -sediment provenance and tectonic studies

Summary The Ordovician of the Rügen area shows no affinities with that of the adjacent regions of the East European Platform, situated immediately to the north (i.e. Bornholm and Skåne). By contrast, the detritus in the sandstones and greywackes points to an active continental margin in the southwest, along the southern border of the suspect Tornquist Ocean (i.e. northern Peri-Gondwana). Deformation features can be assigned to Caledonian tectonic events. The more than 3 km thick pile comprises a stacked wedge complex, which was emplaced against and onto the southwestern border of Baltica.     

Microstrain stability of Peninsular India 1864–1994

We report the results of the South Indian Strain Measuring Experiment (SISME) designed to determine whether strain related to microseismicity in the past century may have deformed the networks of the 19th century Great Trigonometrical Survey of India (GTS). More than a dozen GTS points were measured between Mangalore, Madras, and Kanyakumari in southernmost India using GPS geodesy to determine regional deformation. Detailed measurements were made near two of the original baselines of the survey to determine the reliability of dilatational strain data for the network. The regional measurements revealed negligible regional dilatational (+ 11.2 + 10 microstrain) and shear strain changes (0.66± 1.2μradians) in the southernmost 530 km of India. In addition to these measurements, we determined the rate of northward and eastward motion of a point in Bangalore (1991–1994) in the ITRF92 reference frame to be 39 ± 3.5 mm/year, and 51 ± 11 mm/year respectively. This is consistent with NUVEL-1A plate motion estimate for India. Simultaneous measurements to a point near Kathmandu reveal that the Indian plate and the Southern Himalaya are moving approximately in unison, placing an upper limit on the rate of creep processes beneath the lesser Himalaya of ≈6 mm/year, and suggesting relatively rigid behavior of the Indian plate north of Bangalore. The stability of the Indian plate is confirmed by the absence of significant changes in the lengths of the two baselines at Bangalore and Cape Comorin, which, within the limits of experimental error have not changed since 1869. The measurements place an upper limit for recent deformation in the southern peninsula, and hence a lower limit for the renewal time for intraplate earthquakes in the region of approximately 10,000 years, assuming shear failure strain of approximately 100 μradians. This, in turn, implies that recurrence intervals for Peninsular Earthquakes far exceed the length of the written historic record, suggesting that the characterisation of seismic recurrence intervals from historical studies is likely to be fruitless. In contrast, the SISME experiment demonstrates that the noise level of geodetic studies based on 19th century GTS data is less than 0.02 μstrain/year, providing considerable scope for delineating regions of anomalously high seismogenic strain, by GPS measurements at all available trig points of the 19th century GTS survey.     

Die Entstehung von Pyrit in rezenten Sedimenten des Piburger Sees

The occurrence of pyrite (FeS₂) and iron sulfide in surficial sediments of Piburger See was compared with thermodynamic calculations based on chemical analyses of iron and hydrogen sulfide in the interstitial water. The area below 17 m, where black spots were found in the sediments, showed ion products (log K_FeS=a_Fe2·a_HS/a_H+) between?3.11 and ?4.01. In areas with no visible FeS concretions logK_FeS values were in the range of ?4.74 to ?5.77, thus thermodynamic calculations seem to be in accordance with the appearance of iron sulfide. Nevertheless pyrite framboids, composed by more than 1,000 single crystals, coul be found even in shallow parts of the lake. Therefore the formation of pyrite is assumed to occur in microniches (diatom frustules, testacean shells). Inside these microcompartments high concentrations of hydrogen sulfide are reached due to the anaerobic decomposition of organic matter, whereas iron and additional sulfur are supplied by the diffusion of ferrous iron and sulfate from the anoxic environment.     

Normal faulting of the Daiichi-Kashima Seamount in the Japan Trench revealed by the Kaiko I cruise, Leg 3

A detailed topographic and geophysical survey of the Daiichi-Kashima Seamount area in the southern Japan Trench, northwestern Pacific margin, clearly defines a high-angle normal fault which splits the seamount into two halves. A fan-shaped zone was investigated along 2–4 km spaced, 100 km long subparallel tracks using narrow multi-beam (Seabeam) echo-sounder with simultaneous measurements of gravity, magnetic total field and single-channel seismic reflection records. Vertical displacement of the inboard half was clearly mapped and its normal fault origin was supported. The northern and southern extensions of the normal fault beyond the flank of the seamount were delineated. Materials on the landward trench slope are displaced upward and to sideways away from the colliding seamount. Canyons observed in the upper landward slope terminate at the mid-slope terrace which has been uplifted since start of subduction of the seamount. Most of the landward slope except for the landward walls aside the seamount comprises only a landslide topography in a manner similar to the northern Japan Trench wall. This survey was conducted on R/V “Jean Charcot” as a part of the Kaiko I cruise, Leg 3, in July–August 1984 under the auspices of the French-Japanese scientific cooperative program.     

Monitoring of the integrated column of hydrogen fluoride above the Jungfraujoch Station since 1977 — the HF/HCl column ratio

The amount of hydrogen fluoride (HF) above the International Scientific Station of the Jungfraujoch (Switzerland) has been monitored during the last 8 years. The results deduced spectro-scopically from solar IR absorption measurements near 2.48 m indicate a cumulative trend equivalent to (8.5±1)% increase per year, as well as short-term variability which appears to be strongly correlated with meridional circulation patterns during the February–April months. Based on intensified measurements made over the last three years, it is found that the integrated content of HF undergoes a seasonal change with a minimum occurring in the fall. The HF/HCl ratio derived from simultaneous HF and HCl measurements was found equal to 0.15 during the period 1977–79, and 0.24 for the 1983–85 timespan.     

Sur l'origine de la pyrite et des skarns du gisement,en contexte evaporitique,de Niccioleta (Toscane,Italie)

Résumé La métasomatose d'infiltration par des solutions chlorurées a formé le gisement de Niccioleta, entre 425°C-500 bars et 475°C-1000 bars. Les transformations des substrats (anhydrite, dolomie, micaschistes) révèlent les mécanismes mis en jeux, et l'évolution de la composition des fluides. Les variations de composition du solvant (XCO₂, XH₂O, XH₂S, fS₂, fO₂) expliquent le rôle prépondérant des roches «fluides», carbonates et sulfates, dans la métallogénie hydrothermale. Le transport de Fe est lié à une sous-saturation en Na, K et Ca d'un fluide évoluant à Cl constant. Son dépôt résulte de réactions avec des roches contenant ces éléments; leur dissolution provoque la précipitation du Fe, moins soluble que Na, K et Ca sous forme chlorurée. L'action des carbonates et des sulfates est double: Ca agit sur l'équilibre des chlorures dissous; CO₂, ou H₂S, sur le solvant. Les conséquences de la succession des transformations sont claires dans le cas du sulfate: un fluide «secondaire», s'écoulant d'une zone de dédolomitisation, riche en CO₂ et sous-saturé en silice, transforme l'anhydrite en pyrite; un fluide «primaire» forme de l'andradite. Le fluide originel, «primaire», est une solution aqueuse chlorurée (0,9 à 1,8 m NaCl), réductrice, acide, chargée en Fe et en silice, légèrement soussaturée en Na, K et Ca. Au Miocène sup., le système géothermique régional, ancêtre de celui de Larderello, a été alimenté par des solutions marines, probablement même par des saumures évaportiques messiniennes. L'arrêt de l'activité métallogénique est corrélé à l'émersion du Sud de la Toscane au début du Pliocène. L'anhydrite fait de Niccioleta un cas particulier; le modèle géothermal proposé est plus général. Ses mécanismes sont applicables à de nombreuses minéralisations formées à partir de fluides chlorurés, à haute pression et température.

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The infiltration metasomatism by chloride solutions, between 425°C-500 b and 475°C-1,000 b, has made the pyrite ore-deposit of Niccioleta. The transformations of the substrates (anhydrite-rocks, dolostones, mica schists) show the mechanisms of metasomatism and the fluid composition evolution. Changes of composition of the solvent (XCO₂, XH₂O, XH₂S, fS₂, fO₂) are very important and explain the preponderant action of fluid rocks, such as carbonated and sulfated rocks, in hydrothermal metallogenesis. The carriage of Fe is related to a low undersaturation in Na, K and Ca of a fluid with a constant chloride charge. It deposition results of reactions with Na-, K- or Ca-rich rocks; their dissolving induces the precipitation of Fe, less soluble than Na, K and Ca in chloride fluids. The effects of carbonated and sulfated rocks are double: Ca on the chloride equilibria, CO₂ or S species on the solvent. The importance of successive transformations is well shown in the case of the anhydrite: a secondary fluid, going out of a dedolomitization zone, CO₂-rich and silica undersaturated, changes the sulfate into pyrite; a primary fluid gives andradite. The original, primary, fluid is a reducing and acid chloride aqueous solution (0.9 to 1.8 m NaCl), Fe- and silica-rich, CO₂-poor, and lightly undersaturated in Na, K and Ca.During the Upper Miocene, the regional geothermal system, ancestor of the Larderello one, has been feeded by marine waters, and probably by the messinian evaporitic brines. The end of the metallogenic activity is closely correlated with the emergence of South Tuscany in the Early Pliocene. If the anhydrite-rocks makes Niccioleta to be a peculiar case, the geothermal metallogenic model proposed has a more general interest. Its mechanisms seem to be applicable to numerous mineralizations made by aqueous chloride solutions at high temperatures and pressures.

     

To accrete or not accrete,that is the question

Along modern convergent margins tectonic processes span a spectrum from accretion to erosion. The process of accretion is generally recognized because it leaves a geologic record, whereas the process of erosion is generally hypothetical because it produces a geologic hiatus. Major conditions that determine the dominance of accretion or erosion at modern convergent margins are: 1) rate and direction of plate convergence, 2) sediment supply and type in the trench, and 3) topography of the subducting ocean floor. Most change in structure has been ascribed to plate motion, but both erosion and accretion are observed along the same convergence margin. Thus sediment supply and topography are probably of equivalent importance to plate motion because both erosion and accretion are observed under constant conditions of plate convergence.The dominance of accretion or erosion at a margin varies with the thickness of trench sediment. In a sediment flooded trench, the proportions of subducted and accreted sediment are commonly established by the position of a decollement along a weak horizon in the sediment section. Thus, the vertical variation of sediment strength and the distribution of horizontal stress are important factors. Once deformation begins, the original sediment strength is decreased by sediment remolding and where sediment thickens rapidly, increases in pore fluid pressure can be pronounced.In sediment-starved trenches, where the relief of the subducting ocean floor is not smoothed over, the front of the margin must respond to the topography subducted as well as that accreted. The hypothesized erosion by the drag of positive features against the underside of the upper plate (a high stress environment) may alternate with erosion due to the collapse of a margin front into voids such as graben (a low stress environment).

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Zusammenfassung Entlang modernen konvergierenden Plattenrändern können tektonische Prozesse ein weites Spektrum von Anlagerung bis Erosion umspannen. Der Prozeß der Anlagerung wird generell erkannt, weil er eine geologische Folge aufbaut. Demgegenüber bleibt der Prozeß der Erosion im allgemeinen hypothetisch, weil er einen Hiatus hinterläßt. Die wesentlichen Bedingungen, die das Vorherrschen von Anlagerung oder Erosion bestimmen, sind: 1) Richtung und Rate der Plattenkonvergenz. 2) Sedimentlieferung und-art im Graben. 3) Topographie des subduzierenden Ozeanbodens. Die meisten Wechsel in der Struktur werden der Plattenbewegung zugeschrieben, aber sowohl Erosion als auch Anlagerung sind an demselben konvergierenden Plattenrand beobachtet worden. Daher sind wahrscheinlich die Sedimentanlieferung und die Topographie von gleichrangiger Bedeutung im Hinblick auf die Plattenbewegung, weil Erosion und Anlagerung unter konstanten Bedingungen von Plattenkonvergenz beobachtet werden.Das Vorherrschen von Anlagerung oder Erosion entlang einem Plattenrand variiert mit der Mächtigkeit der Grabensedimente. In einem sedimentbeladenen Graben werden die Verhältnisse von subduzierten und angelagerten Sediment im allgemeinen etabliert durch die Lage einer Abschiebung entlang einem schwachen Horizont innerhalb des Sedimentstapels. Daher sind die Variation der Sedimentfestigkeit in der Vertikalen sowohl als auch die Verteilung der horizontalen Spannungen bedeutende Faktoren. Sobald die Deformation beginnt, nimmt die ursprüngliche Sedimentfestigkeit ab durch die Umgestaltung des Sediments und dort, wo die Sedimentmächtigkeit rasch zunimmt, steigt der Porenwasserdruck deutlich an.In sedimentarmen Gräben, wo das Relief des subduzierten Ozeanbodens nicht ausgeglättet wird, muß die Front des Plattenrandes sowohl auf die subduzierte Topographie reagieren als auch auf die der Anlagerungsgefüge. Die hypothetische Erosion durch den Widerstand der positiven morphologischen Formen gegenüber der Unterseite der höher gelegenen Platte (ein environment hoher Spannungen) kann alternieren mit Erosion, die auf dem Kollabieren eines Plattenrandes in Hohlräume wie etwa in Gräben hinein beruht (ein environment niedriger Spannungen).

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Résumé Le long des bords des plaques convergentes actuelles, l'action tectonique couvre une gamme de processus qui va de l'accrétion à l'erosion. Un processus d'accrétion est d'ordinaire démontré par les traces géologiques qui qu'il laisse, tandis qu'un processus d'érosion, engendrant un hiatus géologique, est geéralement hypothétique. Les principales conditions qui déterminent la prédominance de l'un ou de l'autre processus sont: 1) la cinématique (vitesse et direction) de la convergence; 2) la quantité et la nature de l'apport sédimentaire dans la fosse; 3) la topographie du fond océanique en voie de subduction. La plupart des changements de structure ont été rapportés à la cinématique des plaques. Cependant des actions d'érosion et d'accrétion sont observés le long d'une même bordure convergente; par conséquent l'apport sédimentaire et la topographie océanique jouent probablement un rôle aussi important que la cinématique des plaques.La prédominance de l'accrétion ou de l'érosion le long d'une jonction dépend de l'épaisseur des sédiments de la fosse. Dans une fosse remplie de sédiments, les proportions de sédiments subductés et accrétionnés sont communément déterminés par la position, dans la série sédimentaire, d'un horizon peu résistant le long duquel s'opère un décollement. Il en résulte que les variations verticales de compétence des sédiments et la distribution des contraintes horizontales sont des facteurs importants. Dès que la déformation commence, la résistance mécanique originelle des sédiments est abaissée par leur fluage et, là où les sédiments s'épaississent rapidement, il peut y avoir accroissement marqué de la pression des fluides intersticiels.Dans des fosses pauvres en sédiments, et lorsque le relief du fond océanique en subduction n'est pas aplani, la position du contact des plaques doit résulter autant de la topographie de la plaque descendante que de celle de la plaque supérieure. L'érosion hypothétique due à l'entraînement de formes de relief sous la plaque supérieure (situation de contraintes élevées) peut alterner avec une érosion due à l'effondrement du bord de la plaque par un mécanisme de type «>graben»< (situation de contraintes basses).

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The average molecular weight and shape of the “polymeric acids” found in Black Trona Water from the Green River Basin

Macromolecular organic material, called “polymeric acids”, has been isolated from Black Trona Water by exhaustive dialysis and characterized as the sodium salt in 0.10 M sodium carbonate, pH 10, by several physico-chemical methods. Analysis by gel filtration chromatography on Sepharose-CL 6B indicates that the “polymeric acids” are polydisperse and composed of species of relatively high molecular weight ( 4 × 10⁵, using proteins as standards). With this method, the range of molecular weights appears to be rather narrow. If “polymeric acids” are transferred from sodium carbonate, pH 10, into distilled water, selfassociation occurs and all species elute in the void volume. The weight-average molecular weight determined in 0.10 M sodium carbonate, pH 10, by the light scattering method is 1.7 × 10⁵. Sedimentation velocity analysis at 20°C with the analytical ultracentrifuge gives a value for S_20,w of 5.4 and the shape of the Schlieren patterns suggest a polydisperse sample with a relatively narrow range of sizes. Analysis of the molecular weight distribution by a sedimentation equilibrium method indicates that the range of molecular weights is 8 × 10⁴ to 2.1 × 10⁵. The partial specific volume ( ) of “polymeric acids” is 0.874 ml/g. Viscosity measurements yield a value for [η] of 2.5 ml/g, which indicates that the “polymeric acids” are compact (spherical or ellipsoidal) in shape.     

Dissolved aluminium in interstitial waters of recent marine sediments

Measurements of the concentration and vertical distribution of dissolved aluminium and silica, and of pH. in interstitial waters of recent marine sediments from the North Sea and the Mediterranean Sea were performed to evaluate the behaviour of aluminium during early diagenesis. The results suggest that thermodynamic equilibria alone do not control the concentrations of dissolved species in the system Al-Si-O₂-H₂O during early diagenesis. Rather, these concentrations are governed by dynamic factors involving mineral dissolution-precipitation reactions and diffusion.     

Effect of deposit feeders on migration of137Cs in lake sediments

Illite clay particles with adsorbed¹³⁷Cs were added as a submillimeter layer to the surface of silt-clay sediments contained in rectangular Plexiglas cells stored in a temperature-regulated aquarium, in order to trace the effect of the oligochaete, Tubifex tubifex, and the amphipod, Pontoporeia hoyi, on mass redistribution near the sediment-water interface. A well-collimated NaI gamma detector scanned each sediment column (～10 cm deep) at daily or weekly intervals for six months, depicting the time evolution of radioactivity with and without added benthos. In a cell with tubificids (～5 × 10⁴ m^?2), which feed below 3 cm and defecate on surface sediments, the labeled layer was buried at a rate of 0.052 ± 0.007 cm/day (20°C). When labeled particles entered the feeding zone,¹³⁷Cs reappeared in surface sediments creating a bimodal activity profile. In time, the activity tended toward a uniform distribution over the upper 6 cm, decreasing exponentially below to undetectable levels by 9 cm. In a cell with amphipods (～1.6 × 10⁴ m^?2) uniform activity developed rapidly (～17 days) down to a well-defined depth (1.5 cm). The mixing of sediments by Pontoporeia is described by a simple quantitative model of eddy diffusive mixing of sediment solids. The value of the diffusion coefficient, 4.4 cm²/yr (7°C) was computed from a least squares fit of theoretical to observed profile broadening over time. In a cell without benthos, small but measurable migration of¹³⁷Cs indicated an effective molecular diffusion coefficient of 0.02 cm²/yr.