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131.
L.M. Jones Raymond L. Walker S.E. Kesler John F. Lewis 《Earth and Planetary Science Letters》1979,43(1):112-116
Initial87Sr/86Sr ratios have been determined for a representative suite of Upper Cretaceous granodiorites and associated rocks from the Above Rocks composite stock in central Jamaica and the Terre-Neuve pluton in northwestern Haiti. The average initial87Sr/86Sr ratio for severn samples of the Terre-Neuve intrusion is 0.7036, with a range of 0.7026–0.7047. For two samples of the Above Rocks the initial ratios are 0.7033 and 0.7034. A third sample from this intrusive has an initial ratio of 0.7084, which is tenatively attributed to contamination. The initial87Sr/86Sr ratios indicate that neither ancient sialic crust nor sediments carried down a Benioff zone can be the primary source of the granodioritic magma. K/Rb ratios for these rocks range from 178 to 247, which are much lower than the average values (≥1000) for tholeiitic basalts. It is concluded that the magmas originated primarily by melting of downthrust oceanic crust or adjacent mantle material. 相似文献
132.
133.
The mobility of the rare earth elements: Evidence and implications from selected terrains affected by burial metamorphism 总被引:1,自引:0,他引:1
Phillip L. Hellman Raymond E. Smith Paul Henderson 《Contributions to Mineralogy and Petrology》1979,71(1):23-44
The mobility of the rare earth element (REE) during hydrous burial metamorphism is described from three localities. Comparison of REE abundances in relict domains and metadomains from flood lavas in the Maddina Volcanics, Fortescue Group, Western Australia shows that, relative to the relict domains, REE may be strongly depleted in certain metadomains. Strong variations in La/Yb, La/Sm and Eu may also occur due to postcrystallization secondary processes. Similar comparisons in flood lavas from Mamainse Point in the Canadian Keweenawan Series show that REE are mobile and increase in abundance in metadomains. Spilites from U.S. Virgin Islands also show evidence for REE mobility during low grade burial metamorphism. In this case light REE (LREE) have been preferentially mobilized with heavy REE (HREE) remaining parallel or sub-parallel on chondrite normalized plots.REE analyses from these locations together with an evaluation of published work suggests that the mobility of REE can be described by: 1. gross REE and selective LREE enrichment; 2. REE movement around a primary mean; 3. gross REE depletion; 4. selective REE mobility. Failure to take into account REE mobility may lead to incorrect conclusions concerning petrogenetic models based on altered basic sequences. The coherence of REE with other key trace elements during alteration is also discussed. 相似文献
134.
Techniques have been developed to prepare reasonably homogeneous, reproducible bulk samples of a kaolinite clay (Hydrite 10) with predetermined microfabrics and to reliably identify these microfabrics both quantitatively and qualitatively. Eight samples with quite diverse histories were produced in the laboratory by controlling the chemistry of the clay-water system, the consolidation stress path (either isotropic or anisotropic), and the magnitude of the consolidation stresses. The fabrics of these samples are identified and quantified by the combined use of scanning electron microscopy, optical microscopy, and X-ray diffractometry, and reasonably comprehensive appraisals of particle associations and orientation are obtained. Anisotropic consolidation was found to induce a preferred particle orientation, whereas isotropic consolidation tended to provide basically random samples. The anisotropically consolidated samples from dispersed slurries exhibited somewhat greater particle orientation than those from flocculated slurries, and, although considerable particle orientation occurred at low values of the consolidation stress, increases in the major principal consolidation stress did accentuate the particle orientation. The presence of domains or small groups of particles is suggested in certain samples, especially in those consolidated isotropically. 相似文献
135.
Glenn M. Thompson David N. Lumsden Raymond L. Walker Joel A. Carter 《Geochimica et cosmochimica acta》1975,39(9):1211-1218
Because stalagmites are enriched in 234U beyond the equilibrium value at the time of deposition, they are potentially datable by measuring their progress toward equilibrium. Procedures for uranium-thorium and uranium disequilibrium dating of speleothems were developed, making use of alpha spectrometry for thorium determinations and mass spectrometry for uranium determinations. The stalagmites tested were generally beyond the age range of the U-Th age dating method and, as a result, 234U/238U ratios provided the most useful dating technique. The estimated age range for a stalagmite from Blanchard Springs is 135,000 to 785,000 years BP with an interval of slow or suspended growth from about 320,000 to 570,000 years BP. 相似文献
136.
Résumé On montre d'abord que la théorie des perturbations, due à l'un de nous, conduit à une équation aux dérivées partielles pour les variations de pression au niveau de la mer. Cette même équation peut aussi être déduite par une méthode purement analytique en se basant sur quelques propriétés générales de l'intégrale de Fourier de la perturbation de pression. La méthode utilisée montre d'ailleurs que d'autres fonctions (température, vent, etc.) satisfont aussi à l'équation dont il s'agit. Cette équation de base peut être résolue dans le cas analytique et dans le cas général non analytique et les opérations mathématiques que comporte la solution (opération d'advection par un champ vectoriel horizontal, opération d'intégration pondérée suivant les méridients et son inverse) peuvent être effectuées rapidement et simultanément par l'électronique, ce qui nous a conduit à la construction d'un calculateur analogique approprié à la prévision mathématique du temps à courte et assez longue échéance.
Certaines parties de ce mémoire ont été communiquées le 10 Avril 1953 à la 1.ère Assemblée de la «Società Italiana di Geofisica e meteorologia» (Gênes, 10–12 Avril 1953). 相似文献
Summary The first part of the paper is devoted to the theory of the partial differential equation which is the mathematical foundation of the computer, as well as to the deduction of its general solution.The basic equations of our hydrodynamical theory of perturbations are first of all derived and then associated with the equations of motion and continuity, thus giving the fundamental system of the equations of the atmospheric perturbations. A new form of the kinematical condition on the sea level surface is then derived and applied to give the final equation of the pressure variations. This equation, with its advective and development terms, has two horizontal vectorial coefficients: the one is an advection vector defined as the geostrophic velocity associated with the field of the mean temperature (for a period such that the time variations of the corresponding mean are negligible compared with the variations of the observed temperature); the other coefficient is an horizontal vector having the dimensions of a length, varying as cotg , directed towards north, its streamlines being the geographical meridians.The same partial differential equation can also be deduced by a pure analytical method based on some properties of the Fourier transform of the pressure perturbation. This method also shows that other functions than pressure (temperature, wind, for instance) fulfill the same basic equation on any level surface of gravity.The solution of this equation can be written both in the analytical and in the general non analytical cases, and the second part of the paper shows that the mathematical operations appearing in its expression (advection operation by an horizontal vector field, weighted meridional intergration and its inverse) can be rapidly and simultaneously performed by electronic means, thus leading to the construction of an analogue computer for the short and extended range mathematical weather forecasting.
Certaines parties de ce mémoire ont été communiquées le 10 Avril 1953 à la 1.ère Assemblée de la «Società Italiana di Geofisica e meteorologia» (Gênes, 10–12 Avril 1953). 相似文献
137.
The two known massive Cu-Zn sulphide deposits in the steeply dipping strata of the Golden Grove District of Western Australia — the Gossan Hill Deposit and Scuddles Prospect — both have a multi-element secondary geochemical dispersion halo in the pisolitic layer of laterite of probable Tertiary age. The Gossan Hill geochemical anomaly is about 1.5 × 2 km and has a Bi-Sn-Mo-In-Sb-As-Cu-Au association. Mean compositions of pisolitic laterite samples range from 4 to 18 times background, with maxima for Bi, Sn and Mo reaching 90 to 100 times background. Relief of Gossan Hill, which rises some 80 m above the laterite plain, would have favoured dispersion during lateritization. Nevertheless at Scuddles, where the laterite surface has only a gentle slope across strike, an anomaly in pisolitic laterite measures 1 to 1.5 by 1.5 to 2.0 km. The anomalous association, Bi-Sn-Mo-Sb-As, is similar to that at Gossan Hill; the mean contents in pisolitic laterite samples from the Scuddles anomaly range from 2.3 to 8 times background, with maxima for Bi being 12 times background.At Gossan Hill, individual pisolites and the concretionary skins contain gossan fragments and cassiterite, indicating mechanical dispersion during interitization. However, anomalous Cu, Zn and As in goethites of the concretionary skins of pisolites and nodules from the centre of the anomaly indicate that there has also been hydromorphic dispersion.The geochemical characteristics of pisolitic laterite samples have been represented by empirically derived additive indices based on up to eleven chalcophile elements. One index is suggested as a method to increase anomaly size and simplify interpretation; a more specific index based on Bi, Sn and Se is suggested for defining more closely the actual centres of mineralization.For routine exploration of lateritic terrain where the dips of the host sequence are steep, 320-m spacing of samples on a triangular grid appears suitable for locating anomalies and generally defining their source. However, for reconnaissance exploration, the density of sampling could be significantly reduced for example to 1 km spacing. 相似文献
138.
139.
Ismaı̈la Ngounouno Bernard Déruelle Daniel Demaiffe Raymond Montigny 《Comptes Rendus Geoscience》2003,335(3):289-296
Dykes of monchiquites of Cainozoic age (37.5±2.3 Ma) are intrusive in Cretaceous sandstones in the Tchircotché area, Upper Benue valley (northern Cameroon). The differentiation of the monchiquites is explained by crystal fractionation of olivine, clinopyroxene, magnetite, ilmenite and apatite. A studied rock has low Sr-isotope ratio , which is similar to those of the alkali basalts of the Cameroon Line. Therefore the continental crust appears to have no significant role in the genesis of the monchiquites. 相似文献
140.
We measured organochlorine residues in three species of sea turtles from the Baja California peninsula, Mexico. Seventeen of 21 organochlorine pesticides analyzed were detected, with heptachlor epoxide and gamma-hexachlorocyclohexane the most prevalent (14 (40%) and 11 (31%) of the 35 tissue samples, respectively). PCBs were detected in all but one of the 9 turtles studied, with congener 18 the most commonly detected (8 (23%) of the samples). The dioxin-like congeners 118 and 180 were detected in 4 (11%) and 3 (9%) of the samples, respectively. Percent contribution of congeners was negatively correlated to their octanol-water partition coefficients, with kidney and muscle containing more lower-chlorinated congeners than liver or adipose samples. Levels of organochlorines detected in the present study were low, potentially attributable to the feeding habits of the predominant species collected in this study (herbivorous) and/or the samples obtained in an unindustrialized region. 相似文献