Seismotectonics of the Papua New Guinea—Solomon Islands region

Earthquakes for the period 1964–1973 are relocated by the method of Joint Hypocenter Determination in order better to resolve the configuration and the structure of the New Guinea—New Britain—Solomon Islands region. Focal mechanism solutions are integrated with the seismicity and interpreted closely with it. A zone of subduction exists beneath New Britain and the Solomon Islands, a zone of left-lateral strike-slip movement extends from New Ireland to New Guinea. The zone of seismicity in northern New Guinea has developed as a result of a continent—island-arc collision in late Oligocene—Miocene times and does not exhibit a well-developed inclined seismic zone. It is proposed that plate tectonics theory does not apply rigorously, but slip-line field theory allows the presentation of a new geodynamic model for this region.     

Modified equations for the determination of odd zonal harmonics

The development of the analytical theory of the motion of an artificial satellite (Berger, 1972–1975) points out the great importance of the second, third order and coupling terms between zonal harmonics. These terms have been added to the equations established byKing-Hele andCook (1968–1973) for the determination of odd zonal harmonics. This solution is compared with theirs. It satisfies all the equations much better and especially the equations relating to near-critical inclination satellites.     

Composition isotopique du strontium d'eaux interstitielles extraites de sédiments récents: un argument en faveur de l'homogénéisation isotopique des minéraux argileux

The ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio of interstitial waters squeezed from recent sediments of the Pacific Ocean increases from 0.70920 ± 0.00017 (2σ) to 0.70960 ± 0.0023 and 0.70984 ± 0.00040 at 1.50 and 1.60 m depth—reference value for sea water: 0.70910 ± 0.00035. This variation underlines the likely existence of exchanges between the clays and the interstitial environment. The isotopic homogenization of strontium between the clays and their environment, result of these changes, becomes thus a credible phenomenon. This is a new argument for the dating of clays by the $\text{Rb}\text{Sr}$ method.     

Rythme sedimentaire et mineralisations stratiformes dans l'environnement recifal

During the International Sedimentological Congress of Heidelberg (Germany), the author — in collaboration with his college J.Pel of the University of Liege (Belgium) — has emphasized the influence of the sedimentary rhythm about the location of the stratiform ore deposits in some facies of the reef environment and has proposed a first synthesis of the relations between several stratiform deposits of varying mineralogy and different ages also associated with reef complexes. In this paper, the author illustrates the sedimentological method used previously in resting principally on a comparative analysis of the ore conditions which characterize the stratiform lead zinc deposits of Reocin (Spain), Eastern Alps (Bavaria, Austria), Pine Point (Canada) and S. E. Missouri (United States).     

Un réseau fluviatile d'âge Burdigalien terminal dans le Sud-Est de la France : remplissage,extension, âge,implications

An integrated study combining facies analysis, multiple group biostratigraphy, identification of depositional sequences and mapping has been conducted on the Miocene Molasse Basin of the external Alps (southeastern France). The filling of the basin is described as resulting from a succession of fluvial incisions subsequently filled during marine transgressions. The major incision is dated as Latest Burdigalian and the major transgression as Langhian. This revised interpretation of the Miocene physiographic evolution of the Molasse Basin implies a re-examination of previous stratigraphic correlations within the basin. To cite this article: D. Besson et al., C. R. Geoscience 337 (2005).     

Time-domain boundary element method in viscoelasticity with application to a spherical cavity

The weighted-residual technique, the indirect boundary element method, the truncated indirect boundary element method and the direct boundary element method can be used to analyse nonlinear soil-structure interaction in the time domain. They are illustrated and compared by using the one-dimensional dynamic problem of the spherical cavity in an infinite space. For realistic time steps, all formulations lead to accurate results, but the weighted-residual technique and the truncated indirect boundary element method are much more efficient than the direct boundary element method in the time domain. Hysteretic damping leads to noncausal behaviour, which can, however, be neglected from a practical point of view.     

Non-linear soil–structure interaction analysis based on the boundary-element method in time domain with application to embedded foundation

The various boundary-element methods, well established in the frequency domain, are developed in the time domain for a foundation embedded in a layered halfspace. They are the weighted-residual technique and the indirect boundary-element method, based on a weighted-residual equation, and the direct boundary-element method based on a reciprocity equation, both equations involving time and space. In the indirect approach, formulating the weighted-residual equation over the last time step only results in the truncated indirect boundary-element formulation which requires a reduced computational effort. In all cases, convolution integrals occur. The truncated indirect boundary-element method leads to a highly reliable algorithm, as is verified when a linear analysis in the time domain is compared to the corresponding one in the frequency domain. This boundary-element formulation, which is non-local in space and time, represents a rigorous generally applicable method taking into account a layered halfspace in a non-linear soil-structure interaction analysis. As an example, the non-linear soil-structure interaction analysis of a structure embedded in a halfspace with partial uplift of the basemat and separation of the side wall is investigated.     

Geochemistry of the M'Passa Pb-Zn deposit (Niari syncline,People's Republic of the Congo). Arguments in favor of a hydrothermal origin

The Pb-Zn deposits of the M'Passa mine are located on faults running in a Combian (i.e., N50°E) direction. The interpretation preferred by most authors over the last decade is that synsedimentary ore concentrations have been redistributed in the vicinity of fault zones. This paper presents the results of a detailed study of the behavior of 11 metallic elements (V, Mn, Fe, Co, Cu, Zn, Mo, Ag, Cd, Sb, Pb) systematically measured along a well-exposed section (94 samples, in 28 of which As was also measured). Principal component analysis of the data shows a regular decrease in the total metal content with increasing distance from the fault zones; it also brings to light groupings of metallic elements into a group of mobile elements (Pb, Zn, Cd) and a group of less mobile elements (Ag, Cu, Mo, Fe, Co). The latter are concentrated in and near the fault zone. This distribution corroborates a normal thermal zoning of elements issued from the faults rather than a lateral leaching of a preexisting ore concentration down the fault zone. A gradient in Fe content in sphalerite observed over both ore trends could also indicate regularly decreasing thermal conditions during ore formation. In addition, exploratory measurements of sulfur isotopes clearly indicate an ore concentration process different from an euxinic process. Other synsedimentary metal concentrations related to organic matter evolution seem difficult to reconcile with the total residual organic carbon content, and characteristic ratios regarding organic carbon do not show at the present time any relation with organic matter evolution. Rather than assuming that all organic indicators were erased during the geological evolution of the M'Passa deposit, a model is preferred in which local hydrothermal deposition issued from the fault and diffused through specific dolomitic strata. Paleokarstic features may be regarded as passive ore reservoirs or could be the result of alteration associated with hydrothermal fluids.

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Résumé Les concentrations Pb-Zn exploitées à M'Passa sont localisées sur des failles de direction combienne (N50°E). L'interprétation préférée par la plupart des auteurs de la dernière décennie suppose une préconcentration synsédimentaire, redistribuée dans des zones faillées. Les résultats de l'étude détaillée du comportement de 11 éléments métalliques (V, Mn, Fe, Co, Cu, Zn, Mo, Ag, Cd, Sb, Pb), dosés systématiquement le long de coupes continues (94 échantillons, dont 28 d'entre eux dosés aussi en As) ne permettent pas de confirmer cette hypothèse. L'analyse en composantes principales des teneurs met en évidence une décroissance régulière de la teneur en métaux en s'éloignant des zones faillées. Elle permet aussi de mettre en évidence des groupes de métaux dont une famille d'éléments plus mobiles (Pb, Zn, Cd) et une autre famille d'éléments moins mobiles (Ag, Cu, Mo, Fe, Co). Ces derniers sont concentrés préférentiellement à l'intérieur ou à proximité des zones faillées. Cette distribution s'accorderait davantage avec un zonage thermique normal enraciné dans les failles plutôt qu'avec une redistribution per-descensum de concentrations préexistantes. La décroissance régulière de la teneur en Fe de la blende, fonction de la distance à la faille et indépendante du type de minerai, pourrait aussi avoir été accompagnée d'un gradient thermique au cours du dépot. Quelques mesures exploratoires de constitution isotopique du soufre permettent aussi d'écarter une origine euxinique des sulfures. D'autres possibilités de concentration associée à l'évolution de matières organiques paraisent aussi difficiles à concilier avec la teneur résiduelle en carbone organique. L'absence de relation entre rapports organiques caractéristiques et nature du minerai ne permet pas de conclure à une relation avec l'évolution de la matière organique. Donc, plutôt que considérer que tout marqueur organique aurait été effacé au cours de l'évolution géologique postérieure au dépot, on préfère dans l'état actuel des connaissances un modèle apparenté à une précipitation hydrothermale initiée dans les zones faillées et prolongée latéralement dans des nìveaux dolomitiques spécifiques. Les traits paléokarstiques de ces niveaux seraient alors à envisager, soit comme des réservoirs passifs, soit comme le résutat de l'altération d'épontes par des fluides hydrothermaux.

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G. Buffet present address: INRIA, Avenue Emile Hugues, Sophia Antipolis, France-06565 Valbonne Cedex (reprints)     

THE DETERMINATION OF FLUORINE BY PROTON INDUCED GAMMA RAY EMISSION SPECTROMETRY (PIGE) IN EIGHTEEN CHINESE STANDARD REFERENCE SAMPLES OF STREAM SEDIMENTS, SOILS AND ROCKS: GSD 9-12, GSS 1-8 AND GSR 1-6

Eighteen new Chinese standard reference samples (including stream sediments, soils and rocks) have been analysed by an automated proton induced gamma ray emission (PIGE) method for fluorine. Results of determinations are reported and are generally in good agreement with the "usable values" previously published.     

Tensor structure applied to the least-squares method,revisited

The geometrical approach to the least-squares, based on differential geometry with tensor structure and notations, describes the adjustment theory in a simple and plausible manner. The development relies heavily on orthonormal space and surface vectors, and on the extrinsic properties of surfaces linking the two kinds of vectors. In order to relate geometry to adjustments, the geometrical concepts are extended to an n-dimensional space and u- or r-dimensional surfaces, where n is the number of observations, u is the number of parameters in the parametric method and r is the number of conditions in the condition method, with n=u+r. Connection is made to Hilbert spaces by demonstrating that the tensor approach to the least-squares is a classical case of the Hilbert-space approach.