A new type of active margin: the convergent-extensional margin,as exemplified by the Middle America Trench off Guatemala

The results of DSDP Legs 67 and 84, during which a transect of holes was drilled across the Middle America Trench off Guatemala, show no accretion at the front of that subduction zone since early Eocene time. The tectonic evolution of the trench includes extensional structure on the landward as well as the seaward trench slopes. The Guatemalan margin is proposed as the model of a new type of active margin, the convergent-extensional active margin (CE margin).     

Statistical analysis of isotopic ratios in MORB: the mantle blob cluster model and the convective regime of the mantle

A statistical examination of isotopic distributions for MORB from various ocean ridges leads to the “blob cluster model”, in which the oceanic crust accreting at ridges results from the mixing of two components within the ascending mantle. These are (1) upper mantle material and (2) discrete rising blobs of more radiogenic material. The blobs are fractionated to a variable degree and are distributed in the upper mantle circulation in a manner that is related to the spreading rate.(1) Themean values of the isotopic distributions allow us to calculate the probabilities of the two types of material within the mantle. The results show that theproportion of asthenospheric material in the mixtureincreases with the spreading rate, in agreement with the hypothesis of blob dilution within the upper mantle convection.Mass fluxes can be estimated for the rising blobs from these probabilities, which depend on the respective concentrations in the sources of the two types of material. If the blobs originate in the lower mantle, this flux estimation would suggest that a significant part of the lower mantle has been injected into the upper mantle during earth history.(2) Thestandard deviations of the distributions depend on the “efficiency” of the mixing process:the more imbricated are the asthenospheric and blob materials in the mixture,the smaller is theisotopic spread. This efficiency parameter is shown to increase with the spreading rate, as already suggested by previous comparisons between the East Pacific Rise and the Mid-Atlantic Ridge. Moreover, this feature may also be correlated with other data such as ridge bathymetric variations.     

Etude des minéralisations sulfurées du gisement de Salau,Pyrenées (France) et de ses environs

Résumé Les minéralisations du gisement de Salau, Pyrénées (France) comportent, outre la pyrrhotite et la scheelite, de la chalcopyrite, de l'arsénopyrite et de la sphalérite en phases accessoires. Ces sulfures ont été analysés à la microsonde électronique. — Les pyrrhotites sont les seuls sulfures à avoir subi l'influence de la mise en place de la rhyodacite. Les autres sulfures présentent une grande homogénéité et n'ont pas subi de modification liée à la mise en place du pluton. Les teneurs en fer des sphalérites, homogènes à l'intérieur d'un même niveau stratigraphique, mais différentes d'un niveau à l'autre, suggèrent une mise en place à plusieurs périodes sans remaniement ultérieur à leur dépôt.

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Mineralisation of Salau deposit, Pyrénées (France) contain massive pyrrhotite and scheelite associated with chalcopyrite, arsenopyrite and sphalerite. Electron microprobe analyses of these sulfides have been systematically performed. — Pyrrhotites show a zonation with regard to the rhyodacite settlement. Other sulfides show a great homogeneity and are not disturbed by this settlement. Iron content of sphalerites, homogeneous inside a given stratigraphical level but different when the age of layers change, suggest several origins without further modification.

     

An evaluation of Rock-Eval pyrolysis for the study of Australian coals including their kerogen and humic acid fractions

Rock-Eval pyrolysis was performed on lithotype and depth profiles of Tertiary brown coals and a coalification profile of Permian bituminous coals. The humic acid and kerogen fractions from the coals are also investigated by this technique along with the effect of base extraction on the kerogen fraction. Structural variations between brown coal lithotypes are primarily reflected by changes in Oxygen Index Value. This result was supported by the results from the depth profile (same lithotype). A wide range of Hydrogen Indices (independent of depth) but similar Oxygen Indices were observed. The results from the Qualification profile show that the Oxygen Indices varied with rank, whereas Hydrogen Indices show a greater dependence on coal type. A plot of $\text{H}\text{C}$versus Hydrogen Index produced good correlations with the brown (0.77) and bituminous (0.90) samples lying on two separate lines intersecting at high H/C. This result (and higher correlation for bituminous samples) reflects the expected dependence of hydrogen index on oxygen content (present primarily as hydroxyl groups). A high correlation (0.95) between quantitative IR data (K 2920 cm mg^?1) and Hydrogen Indices supports previous conclusions regarding the dependence of Hydrogen Indices on the aliphatic structure of the samples.     

A study of Gd,Ce and Eu impurities in fluorite deposits by electron paramagnetic resonance and neutron activation analysis

In order to obtain a better understanding of fluorite deposits, rare earth impurities have been analyzed for a large number of samples taken from cross-sections of several low temperature hydrothermal veins. Two types of measurements have been used: Electron Paramagnetic Resonance (EPR) and Neutron Activation Analysis (NAA). For Gd, the ratio of spin concentrations to total concentration [Gd³⁺]/[Gd_total] is close to 1 in all the samples; on the other hand, the ratios [Eu²⁺]/[Eu_total] and [Ce³⁺ -F _? ⁱ ]/[Ce_total] exhibit large variations. The first result suggests that the major part of the lanthanides in the samples is incorporated in the crystal lattice and that clustering of lanthanides ions is not important. The behaviour of Eu and Ce is ascribed to charge state changes and symmetry state changes respectively.     

Notes on late Cenomanian and Turonianammonites from Touraine,Western France

Recent collecting in the type area of the Turonian stage and adjacent parts of Touraine in western France provides new geographic and stratigraphic records as well as additional systematic information on species of the ammonite genera Puzosia, Watinoceras, Metoicoceras, Mammites, Prohauericeras, Collignoniceras, Lecointriceras, Subprionocyclus and Sciponoceras.     

Thermal radiation from cloudless skies in Granada

Summary Data on thermal radiation from clear skies obtained at Granada from May to November 1983 were utilized to carry out a detailed comparison between measured and calculated values of longwave radiation with several analytical and empirical equations. The goal of this work is to check the aplicability of these equations to Granada conditions. The results obtained for all the equations are quite satisfactory. Nevertheless, Idso's formula significantly overestimates our experimental results, probably as a consequence of the differences in atmospheric dust conditions between our test area and the location for which that equation was originally derived. A reduction in the independent coefficient, in accordance with previous results of other authors, provides a better fit to our data set and clearly shows the climatological dependence of the constants in the estimation equations.

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Zusammenfassung Die von Mai bis November 1983 in Granada gesammelten Daten über Wärmestrahlung bei klarem Himmel wurden dazu verwendet, um einen detaillierten Vergleich zwischen gemessenen und errechneten Werten der langwelligen Strahlung aus verschiedenen analytischen und empirischen Gleichungen durchzuführen. Das Ziel dieser Arbeit ist es, die Anwendbarkeit dieser Gleichungen auf die Verhältnisse in Granada zu überprüfen. Die gewonnenen Ergebnisse sind für alle diese Gleichungen ganz zufriedenstellend. Idsos Formel überschätzt jedoch deutlich unsere experimentellen Ergebnisse, möglicherweise als Folge der unterschiedlichen atmosphärischen Staubbedingungen in unserem Testgebiet und dem Standort, für den die Gleichung ursprünglich abgeleitet wurde. Eine Reduktion des unabhängigen Koeffizienten, in Übereinstimmung mit früheren Ergebnissen anderer Autoren, bietet eine bessere Anpassung an unseren Datensatz und zeigt deutlich die klimatologische Abhängigkeit der Konstanten in Schätzungsgleichungen.

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Diabatic wind and temperature profiles obtained from a 100 m tower: A statistical comparison of model performances

More than 8000 10-min profiles of wind and temperature obtained during an extensive field experiment have been analyzed. The study was carried out in the environs of Valladolid (Spain) where a 100-m and a 6-m meteorological tower are located. Less than 20% of data were discarded due to equipment failure. Because of its exceptional flatness, the site is almost ideal for model performance comparisons.Predicted profiles of wind speed and potential temperature at 12, 26, 51, and 100 m heights were obtained using the methods proposed by Berkowicz and Prahm (1982) and San José (1983) based on values observed on a 6 m tower. Statistical t, F, and R tests were used to determine bias, scatter and correlation. The data were classified according to atmospheric stratification and height above ground. Finally, a determination was made of the predicted wind speeds and potential temperatures that fell within the 1 and 20% confidence ranges centered at the measured value. San José's method performed better than did that of Berkowicz and Prahm for the temperature profiles in both unstable and stable conditions. However, no significant differences were found for the wind speed profiles.