Interprétation quantitative de l'anisotropie de susceptibilité magnétique

We propose a model in which the magnetic susceptibility anisotropy is considered as resulting from the distinct properties of two rock components. This model suggests that differences in the susceptibility ellipsoid can be principally related to mineralogical variations. Thus, some difficulties in the quantitative interpretation of anisotropy data may be explained. This model is consistent with a detailed analysis carried on Dalradian rocks from Scotland.A new methodology of anisotropy analysis is derived. It is based on the fact that, in specimens from a same sample, the susceptibility ellipsoid often varies, but relations nevertheless exist between values of the principal and mean susceptibilities. For each sample, measurements are made on 6–12 specimens. The study of the relations between principal and mean susceptibilities permits separation of the anisotropies of the rock components, the anisotropy determination appearing the best for the high susceptibility component.

Résumé

L'examen d'un modèle de roche, où l'anisotropie est considérée comme résultant des propriétés de deux constituants, montre que l'ellipsoïde de susceptibilité dépend fortement de la composition minéralogique. Ainsi s'expliquent certaines difficultés de l'interprétation quantitative des résultats d'anisotropie. Ce modèle est testé avec succès sur une série du Dalradien d'Écosse.Une nouvelle méthodologie d'analyse de l'anisotropie en découle. Elle est basée sur la constatation que l'ellipsoïde de susceptibilité présente souvent des fluctuations dans les différents spécimens taillés dans un même échantillon, et que des relations simples existent cependant entre les différentes valeurs des susceptibilités principales et moyenne. Pour chaque échantillon, les mesures sont faites sur 6–12 spécimens. L'étude des relations entre susceptibilités principales et moyenne permet une séparation des anisotropies des constituants de la roche, la détermination de l'anisotropie semblant d'autant meilleure que la susceptibilité est plus forte.     

A paleomagnetic and isotopic age for the Wackerfield Dyke of northern England

The Wackerfield Dyke is exposed in northern England and its field relationships suggest it could be related to the Eocene Mull Dyke Swarm. Wackerfield Dyke specimens taken from below the zone of surface weathering have a natural remanent magnetization that is extremely stable to thermal and alternating field demagnetization. Stability is expected because the Fe-Ti oxides are highly oxidized. The stable magnetization is identical with a primary remanence that can be isolated from certain samples of the Whin Sill of northern England, and gives a mean pole at 175°E, 22°N (dp = 2°, dm = 3°). An Upper Carboniferous age for the Wackerfield Dyke is confirmed by a K-Ar whole rock age of 303 my.     

Recent advances in the chemistry and properties of atmospheric nucleants: a review

Summary A survey is carried out of recent progress in the investigation of weather-active atmospheric nucleants. Emphasis is placed on the work date during the last decade, and some resulting implications are discussed.     

Eclogite xenoliths from stockdale kimberlite,Kansas

Six kimberlite pipes of late Cretaceous or Tertiary age occur in Riley Co., east-central Kansas. Within the pipes xenoliths of local sedimentary and exotic igneous rocks are common, especially in the Stockdale pipe. Igneous rocks which occur as xenoliths include granite, gabbro, metagabbro, pyroxenite and eclogite. In the eclogites omphacitic clinopyroxene (approx. Di₅₂Jd₂₄mol%) and pyropic garnet (approx. Py₄₇Al₃₅Gr₁₂mol%) are the predominant minerals with subordinate amounts of rutile and sulphides (pyrrotite-pentlandite (?)-chalcopyrite). Interstitial kaersutitic amphibole is a minor constituent. The eclogites are chemically equivalent to olivine-basalt. The texture, composition and mineralogy of the eclogites from Kansas are similar to those of eclogites from kimberlite pipes in South Africa and Siberia. Whereas the rocks from these latter localities display a range in composition, those examined to date from Kansas are of fairly restricted composition. Furthermore it seems probable that the eclogites from Stockdale formed under limited P-T conditions within the mantle. This is the first record of such eclogites on the North American continent.     

Effect of chloride concentration on the decomposition of aqueous sodium nitrate by sunlight

Summary Rates and yields of nitrite formation in solutions, upon irradiation of aqueous sodium nitrate with ultraviolet light, are found to be consistently and considerably enhanced by their chloride content. The process is investigated under conditions met both, in the laboratory and under sunlight illumination, and the effects of altitude and temperature on the reaction studied in the field, are evaluated.     

A Re - Assessment of the Criteria for Certifiability in CCRMP

The effect of the between- and within-laboratory standard deviation and of the number of laboratories on the magnitude of the certification factor, CF, introduced in 1975 by the Canadian Certified Reference Materials Project (CCRMP) has been discussed. The applicability of CF to reference materials has been assessed on the basis of the correlation between the between- and within-laboratory standard deviation. The validity of the critical value of 4 for CF for certifiability is examined.
An examination of all available data has led to the conclusion that the quality of an interlaboratory program is sufficient to warrant certifiability only if the ratio of the between-to the within-laboratory standard deviation is 3 or less for most elements and 2 or less for uranium. It has been shown that the number of laboratories rejected based on the upper limit of this ratio differs only slightly from that based on laboratory means differing by more than twice the standard deviation of the overall mean for the majority of elements that have been certified. A new measure for assessing the certifiability of an element has been introduced and is based on the requirement that the percentage of laboratories that are rejected to give a ratio of the between- to within-laboratory standard deviation less than or equal to the critical value of 3 or, for uranium, 2 should be no greater than 15% regardless of the number of laboratories in the certification program.