Représentation graphique de la cristallisation fractionnée des séries volcaniques. Application aux séries alcalines     

J. Leterrier Nancy  R. C. Maury 《International Journal of Earth Sciences》1978,67(3):943-952

Résumé Les modalités de la cristallisation fractionnée des séries volcaniques peuvent Être suivies en reportant sur le diagramme rectangulaire R₁=6 Ca+2 Mg+Al; R₂=4 Si–11 (Na+K)–2 (Fe+Ti), (en nombres de millications dans l'analyse) les compositions des liquides successifs (laves aphyriques) et des phases qui fractionnent (phénocristaux, cumulats). A titre d'exemple d'application sont comparées deux séries alcalines de la Polynésie. La série basalte alcalin-phonolite de l'Île de Rapa (Australes) résulte de la séparation de minéraux du plan critique (olivine-plagioclase-clinopyroxène) du tétraèdre basaltique, alors que dans l'Île de Nuku-Hiva (Marquises) la différenciation conduit à des trachytes quartzifères en raison du fractionnement de phases hydroxylées sous-saturées en silice (amphibole et mica).

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The fractional crystallization sequence of volcanic series can be studied with the rectangular diagram R₁=6 Ca+2 Mg+Al; R₂=4 Si–11 (Na+K)–2 (Fe+Ti), (numbers of millications in the analysis) on which are reported the compositions of successive liquids (aphyric lavas) and fractionating minerals (phenocrysts, cumulates). The usefulness of this diagram is illustrated in the comparison of two alkali basalt series from Polynesia. The alkali basalt-phonolite association of Rapa island (Australs) is a result of the fractionation of minerals belonging to the critical plane (olivine — plagioclase — clinopyroxene) of the basalt tetrahedron. In the Nuku-Hiva (Marquesas) series, the origin of oversaturated trachtytes results from the fractionation of undersaturated hydrous minerals (amphibole and mica).

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Zusammenfassung Der Vorgang einer fraktionierten Kristallisation vulkanischer Reihen kann in folgendem rechtwinkligen Diagramm (Gehalte in Millikationen ausgedrückt) gut verfolgt werden: R₁=6 Ca+2 Mg+Al; R₂=4 Si–11 (Na+K)–2 (Fe+Ti), indem die Zusammensetzung der aufeinanderfolgenden Schmelzen (aphyrische Laven) und der auskristallisierenden Phasen (Phänokristalle und Kumulate) eingetragen werden. Als Anwendungsbeispiel werden zwei Alkali-Reihen aus Polynesian verglichen. Die Reihe Alkali-Basalt — Phonolit der Insel Rapa (Südliche Inseln) entstammt der Abtrennung von Mineralien, die auf der kritischen Ebene (Olivin, Plagioklas, Klinopyroxenen) des basaltischen Tetraeders liegen. Auf der Insel von Nuku-Hiva (Marquesas Inseln) hingegen, führt die Differentiation zu Quartz-Trachyten, bedingt durch die Fraktionierung in SiO₂-untersättigte und Hydroxyl-haltige Minerale (Amphibol und Glimmer).

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Statistical representation of generalized distribution data for float-sink coal-cleaning devices: Baum jigs,Batac jigs,Dynawhirlpools     

Nancy E. Fallon  Byron S. Gottfried 《International Journal of Mineral Processing》1985,15(3):231-236

In an earlier paper (1978), Gottfried presented a method for combining distribution data for float-sink coal-cleaning devices into a single generalized distribution curve which, for a given device and feed size, is independent of specific gravity of separation. A non-linear, exponential-type equation was utilized to represent the generalized distribution curve, along with the corresponding generalized probable error. Distribution data for six common coal-cleaning devices have previously been treated by this method.This paper is an extension of two previous studies (Gottfried, 1978, 1980). The method described above is applied to three different float-sink coal-cleaning devices: Baum jig (replacing previously reported results), Batac jig and Dynawhirlpool separator. Results for the Baum jig and Batac jig reflect a two-stage separation process, with a set of generalized distribution curves obtained for each stage and another set for the overall separation. Several different feed size fractions are given for each vessel.  相似文献   

Respiration rates and hypoxia on the Louisiana shelf     

Quay Dortch  Nancy N. Rabalais  R. Eugene Turner  Gilbert T. Rowe 《Estuaries and Coasts》1994,17(4):862-872

The spatial and temporal variation in water-column respiration, estimated from enzymatic respiratory electron-transport-system activity, was measured monthly on a cross-shelf transect on the Louisiana shelf from May through October 1991. In July 1991, water-column respiration was also determined on an alongshore transect, and in situ benthic respiration and photosynthesis rates were determined at jour stations on the cross-shelf transect. Bottom waters were persistently hypoxic (O₂<2 mg 1^?1) at most stations in July and August and sporadically hypoxic at other times. Water-column respiration rates were in the same range as earlier, less extensive studies and not unusually high for coastal and estuarine waters. They were highest in summer, decreased with distance offshore and depth, and increased with temperature. Their variation with pigment and oxygen concentrations were complex functions of season and depth. Oxygen depletion below the oxycline could occur within days to months, depending on the season and location. In July, benthic respiration rates were also not unusually high in comparison with other shallow sediments, although the ratio of benthic: total (water column+benthic) respiration was high. Combined water-column and benthic respiration could deplete the bottom water oxygen in approximately 1 mo. Because the system rarely goes anoxic (defined as observing sulfide), some mechanism(s) must exist to reaerate bottom waters. Most physical mechanisms are unlikely to provide significant reaeration at this time of year. Measured benthic and conservatively estimated bottom-water photosynthesis could resupply 23% of the oxygen lost daily by respiration. Although this is too limited a dataset from which to draw conclusions about the relative importance of bottom-water and benthic respiration and photosynthesis in determining bottom-water oxygen concentrations, it does suggest that all these processes must be considered.  相似文献   

Distribution of seabirds in the northern Gulf of Mexico in relation to mesoscale features: initial observations   总被引：1，自引：0，他引：1  

Ribic  Christine A.; Davis  Randall; Hess  Nancy; Peake  Dwight 《ICES Journal of Marine Science》1997,54(4):545-551

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The effect of Ni on element partitioning during iron meteorite crystallization     

Nancy L. Chabot  Sarah A. Saslow  William F. McDonough  Timothy J. McCoy 《Meteoritics & planetary science》2007,42(10):1735-1750

Abstract— ‐Iron meteorites exhibit a large range in Ni concentrations, from only 4% to nearly 60%. Most previous experiments aimed at understanding the crystallization of iron meteorites have been conducted in systems with about 10% Ni or less. We performed solid metal/liquid metal experiments to determine the effect of Ni on partition coefficients for 20 trace elements pertinent to iron meteorites. Experiments were conducted in both the end‐member Ni‐S system as well as in the Fe‐Ni‐S system with intermediate Ni compositions applicable to high‐Ni iron meteorites. The Ni content of the system affects solid metal/liquid metal partitioning behavior. For a given S concentration, partition coefficients in the Ni‐S system can be over an order of magnitude larger than in the Fe‐S system. However, for compositions relevant to even the most Ni‐rich iron meteorites, the effect of Ni on partitioning behavior is minor, amounting to less than a factor of two for the majority of trace elements studied. Any effect of Ni also appears minor when it is compared to the large influence S has on element partitioning behavior. Thus, we conclude that in the presence of an evolving S‐bearing metallic melt, crystallization models can safely neglect effects from Ni when considering the full range of iron meteorite compositions.  相似文献   

Post-Clovis survival of American Mastodon in the southern Great Lakes Region of North America     

Neal Woodman  Nancy Beavan Athfield   《Quaternary Research》2009,72(3):359-363

The end of the Pleistocene in North America was marked by a wave of extinctions of large mammals, with the last known appearances of many species falling between ca. 11,000–10,000 ¹⁴C yr BP. Temporally, this period overlaps with the Clovis Paleoindian cultural complex (11,190–10,530 ¹⁴C yr BP) and with sudden climatic changes that define the beginning of the Younger Dryas chronozone (ca. 11,000–10,000 ¹⁴C yr BP), both of which have been considered as potential proximal causes of this extinction event. Radiocarbon dating of enamel and filtered bone collagen from an extinct American Mastodon (Mammut americanum) from northern Indiana, USA, by accelerator mass spectrometer yielded direct dates of 10,055 ± 40 ¹⁴C yr BP and 10,032 ± 40 ¹⁴C yr BP, indicating that the animal survived beyond the Clovis time period and into the late Younger Dryas. Although the late survival of this species in mid-continental North America does not remove either humans or climatic change as contributing causes for the late Pleistocene extinctions, neither Clovis hunters nor the climatic perturbations initiating the Younger Dryas chronozone were immediately responsible for driving mastodons to extinction.  相似文献   

LIBS analysis of geomaterials: Geochemical fingerprinting for the rapid analysis and discrimination of minerals     

Russell S. Harmon  Jeremiah Remus  Nancy J. McMillan  Catherine McManus  Leslie Collins  Jennifer L. Gottfried Jr.  Frank C. DeLucia  Andrzej W. Miziolek 《Applied Geochemistry》2009

Laser-induced breakdown spectroscopy (LIBS) is a simple atomic emission spectroscopy technique capable of real-time, essentially non-destructive determination of the elemental composition of any substance (solid, liquid, or gas). LIBS, which is presently undergoing rapid research and development as a technology for geochemical analysis, has attractive potential as a field tool for rapid man-portable and/or stand-off chemical analysis. In LIBS, a pulsed laser beam is focused such that energy absorption produces a high-temperature microplasma at the sample surface resulting in the dissociation and ionization of small amounts of material, with both continuum and atomic/ionic emission generated by the plasma during cooling. A broadband spectrometer-detector is used to spectrally and temporally resolve the light from the plasma and record the intensity of elemental emission lines. Because the technique is simultaneously sensitive to all elements, a single laser shot can be used to track the spectral intensity of specific elements or record the broadband LIBS emission spectra, which are unique chemical ‘fingerprints’ of a material. In this study, a broad spectrum of geological materials was analyzed using a commercial bench-top LIBS system with broadband detection from ∼200 to 965 nm, with multiple single-shot spectra acquired. The subsequent use of statistical signal processing approaches to rapidly identify and classify samples highlights the potential of LIBS for ‘geochemical fingerprinting’ in a variety of geochemical, mineralogical, and environmental applications that would benefit from either real-time or in-field chemical analysis.  相似文献   

Controls on chemistry and diagenesis of naturally occurring iron-oxide phases     

Nancy W. Hinman  J. Michelle Kotler  Beizhan Yan  Aaron Tenesch  Richard V. Morris  Andrew Tveter  Daphne L. Stoner  Jill R. Scott 《Applied Geochemistry》2009

The purposes of this study were to (i) document chemical and mineralogical compositions in two naturally acidic drainages over a 1 m soil profile, (ii) document organic and inorganic signatures representative of past chemical or biological processes in the soils, and (iii) determine whether mineralogical and chemical differences are a consequence of differences in original composition, depositional conditions, or diagenesis. Two sites were studied: Paymaster Creek in the Heddleston Mining District near Lincoln, Montana and the New World Mining District near Cooke City, Montana. The oldest deposits at both naturally acidic sites pre-date human mining activity by several thousand years, although there is recent human activity at both sites. Both sites have streams with high dissolved Fe and moderately low pH and actively accumulate schwertmannite on streambeds. Soil deposits away from the streambed at Paymaster Creek contained goethite with adsorbed sulfate, but no schwertmannite, suggesting either that the original conditions precluded schwertmannite precipitation or that diagenesis occurred rapidly converting the schwertmannite to goethite. The New World Mining District site showed the expected profile, which is a gradual transition from schwertmannite- and goethite-bearing soils to goethite-only soils. Concentrations of Cr, As and other trace elements shown to retard diagenesis were higher at the New World site than at the Paymaster site.  相似文献   

The significance of the personal within disability geography     

Nancy Worth 《Area》2008,40(3):306-314

Drawing on in-depth qualitative data, this article critically examines disability geography as a subfield where the personal is highly valued. The value and the risks inherent in this personal approach will be evaluated, including the usefulness of being an 'insider' and the difficulties of being reflexive and critically making use of one's positionality. The article concludes with reflections regarding how disability geography can confront its marginal status, appealing to researchers who claim no experience of disability while also supporting and encouraging those with personal experiences of disability to participate in the field.  相似文献   

THE MARBLE BEACHES OF TUSCANY*     

Karl F. Nordstrom  Enzo Pranzini  Nancy L. Jackson  Massimo Coli 《Geographical review》2008,98(2):280-300

ABSTRACT. Beach‐nourishment operations designed to replace sediment lost through erosion change the identity and meaning of coastal landscapes. Seven beaches in Tuscany, nourished with marble‐quarry waste, reveal how an industrial byproduct is naturalized by particle rounding and sorting and can become a positive symbol of human‐altered nature. The marble was placed on formerly sandy beaches, resulting in different grain size and color of sediments, beach morphology, and value for human use. The abrasion rate of marble makes the nourished beaches unsatisfactory when viewed solely as protection structures, but the rapid particle rounding and aesthetic appeal of marble increase the acceptability of the beaches for recreation.  相似文献