The RbSr isotope system as an index of origin and diagenetic evolution of southern Pacific red clays     

Norbert Clauer  Michel Hoffert  Anne-Marie Karpoff 《Geochimica et cosmochimica acta》1982,46(12):2659-2664

Morphological, mineralogical, chemical and RbSr isotopic studies have been made on Fesmectites (nontronites) from southern Pacific red clays cored near the Marquisas Islands. These minerals have at the top of the core, an ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio of 0.70917 ± 0.00007, which indicates an authigenic origin in isotopic equilibrium with seawater. Weak leaching experiments with 1N HCl show that the nontronites also contain a volcanic component with a lower ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio which, combined with the morphology of the particles, suggests a transportation by bottom currents of clay formed elsewhere.During burial, the nontronites experience diagenetic modifications resulting in an increase in Fe, K and Rb contents, a concomitant decrease of Mg, Ca, Ti, Na and Sr, and a preferential migration of radiogenic ⁸⁷Sr from the clays into the surrounding pore waters.The ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratio of the Sr adsorbed on the outermost surfaces of the nontronites does not change with depth in the core, and is, therefore, independent of diagenetic influence, which is rather characterized by the ${}^{87}\text{Sr}{}^{86}\text{Sr}$ ratios of the interstitial waters. The isotopic composition of both the adsorbed Sr and that of the pore fluids may yield useful information on the crystallization environment and subsequent history of deep sea red clays.  相似文献   

Relations entre les concentrations des ions alcalins dans les eaux thermales sulfurées sodiques du Midi de la France     

Grald Ouzounian  Gil Michard  Christian Fouillac  Catherine Beaucaire 《Chemical Geology》1980,30(4):317-339

Alkali ion concentrations were studied in hot sulphurated springs in the south of France. Strong correlations between elements (K-Rb, K-Cs and Na-Li) are found. The element concentrations are also closely related with deep temperature as estimated by classical geothermometers. A discussion of the origin of the interelement correlations is presented. Further studies on the behaviour of trace elements during mineral dissolution are needed and can yield interesting methods of investigation in geothermal exploration.

Résumé

L'étude des concentrations des ions alcalins dissous dans les eaux thermales sulfurées du Midi de la France montrent de très nettes corrélations entre éléments (K-Rb, K-Cs et Na-Li) ainsi que des corrélations entre concentrations d'éléments et température profonde estimée à l'aide des géothermomètres classiques. Plusieurs suggestions quant à l'explication des relations observées sont présentées. Une bonne compréhension du comportement des ions en trace lors de la dissolution des minéraux par l'eau aurait certainement des retombées intéressantes en prospection géothermique.  相似文献   

Metasomatism in the subcontinental mantle beneath the Eastern Carpathians (Romania): new evidence from trace element geochemistry   总被引：9，自引：1，他引：9  

Françoise Chalot-Prat  Anne-Marie Boullier 《Contributions to Mineralogy and Petrology》1997,129(4):284-307

A wide range of trace elements have been analysed in mantle xenoliths (whole rocks, clinopyroxene and amphibole separates) from alkaline lavas in the Eastern Carpathians (Romania), in order to understand the process of metasomatism in the subcontinental mantle of the Carpatho-Pannonian region. The xenoliths include spinel lherzolites, harzburgites and websterites, clinopyroxenites, amphibole veins and amphibole clinopyroxenites. Textures vary from porphyroclastic to granoblastic, or equigranular. Grain size increases with increasing equilibrium temperature of mineralogical assemblages and results from grain boundary migration. In peridotites, interstitial clinopyroxenes (cpx) and amphiboles resulted from impregnation and metasomatism of harzburgites or cpx-poor lherzolites by small quantities of a melt I with a melilitite composition. Clinopyroxenites, amphibole veins and amphibole clinopyroxenites are also formed by metasomatism as a result of percolation through fracture systems of large quantities of a melt II with a melanephelinite composition. These metasomatic events are marked by whole-rock enrichments, relative to the primitive mantle (PM), in Rb, Th and U associated in some granoblastic lherzolites and in clinopyroxene and amphibole veins with enrichments in LREE, Ta and Nb. Correlations between major element whole-rock contents in peridotites demonstrate that the formation of interstitial amphibole and clinopyroxene induced only a slight but variable increase of the Ca/Al ratio without apparent modifications of the initial mantle composition. Metasomatism is also traced by enrichments in the most incompatible elements and the LREE. The Ta, Nb, MREE and HREE contents remained unchanged and confirm the depleted state of the initial but heterogeneous mantle. Major and trace element signature of clinopyroxene suggests that amphibole clinopyroxenites and some granoblastic lherzolites have been metasomatized successively by melts I and II. Both melts I and II were Ca-rich and Si-poor, somewhat alkaline (Na > K). Melt I differed from melt II in having higher Mg and Cr contents offset by lower Ti, Al, Fe and K contents. Both were highly enriched in all incompatible trace elements relative to primitive mantle, showing positive anomalies in Rb, Ba, Th, Sr and Zr. They contrasted by their Ta, Nb and LREE contents, lower in melt I than in melt II. Melts I and II originate during a two-stage melting event from the same source at high pressure and under increasing temperature. The source assemblage could be that of a metasomatized carbonated mantle but was more likely that of an eclogite of crustal affinity. Genetic relationships between calc-alkaline and alkaline lavas from Eastern Carpathians and these melts are thought to be only indirect, the former originating from partial melting of mantle sources respectively metasomatized by the melts I and II. Received: 17 March 1997 / Accepted: 14 July 1997  相似文献   

Resetting of oxybarometers and oxygen isotope ratios in granulite facies orthogneisses during cooling and shearing,Adirondack Mountains,New York     

Ian Cartwright  John W. Valley  Anne-Marie Hazelwood 《Contributions to Mineralogy and Petrology》1993,113(2):208-225

The petrography, petrology, and oxygenisotope geochemistry of granulite-facies granitic and syenitic orthogneisses of the Diana and Stark complexes, Adirondack Mountains, New York, show that the extent and nature of resetting of isotopic and mineralogic systems is highly variable. There is a strong correlation between retrogression and shearing, and the rocks may be divided texturally into: (1) unsheared lithologies that preserve little-retrogressed pyroxene-or hornblendebearing peak-metamorphic mineralogies; and (2) sheared rocks that underwent retrogression, marked by the growth of late biotite, in centimetre-to metre-wide shear zones after the peak of metamorphism. Oxygen fugacities in the unsheared lithologies were estimated for reintegrated mineral compositions from magnetiteilmenite (Mt-Ilm) and ferrosilite-magnetic-quartz (Fs-Mt-Qtz) equilibria. Mt-Ilm yields logfO_2Mt-Ilm values of-15.9 to-17.6 (0.6 to 1.3 log units below the fayalite-magnetite-quartz buffer, FMQ) and temperatures of 670–745°C that agree with those from other geothermometry and phase equilibria studies. These data suggest that, aside from oxyexsolution of ilmenite from magnetite, the Fe-Ti system underwent only minor resetting during cooling, and the Fe-Ti oxides yield good estimates of peak-metamorphic temperatures and fO₂. In unsheared ilmenite + magnetite + orthopyroxene + quartz assemblages, values of logfO_2Mt-Ilm are lower than logfO_2Fs-Mt-Qtz by an average of 0.6 when the orthopyroxene activity model of Sack and Ghiorso is used. Minor resetting of the Fe-Ti oxides, analytical errors, and errors in the placement of end-member reactions probably account for this relatively small difference in fO₂ values. Whole-rock ¹⁸O values of unsheared Diana and Stark lithologies range from 4.0 to 10.3 reflecting pre-regional metamorphic oxygen-isotope ratios. Peak-metamorphic minerals preserve high-temperature oxygen-isotope fractionations, and, in many samples, the effective diffusion of oxygen in minerals ceased at higher temperatures than predicted from wet experimental diffusion data. These data suggest that the rocks did not contain an aqueous fluid phase during cooling. The combination of petrologic, isotopic, and textural data also permits a detailed study of shearing and retrogression. Ilmenites in the sheared lithologies underwent greater degrees of hematite loss than in the unsheared rocks, resulting in logfO_2Mt-Ilm values as low as-24.1 (3.1 log units below FMQ) and Mt-Ilm temperatures that are up to 175°C below regional estimates. Sheared rocks also have higher ¹⁸O values (up to 13.3). During shearing, ¹⁸O values of biotite, K-feldspar, and magnetite reset readily, while the degree of isotopic resetting of quartz correlates with the intensity for recrystallization.This paper is a contribution to IGCP Project 304, Lower Crustal Processes  相似文献   

Oligotrophication from wetland epuration alters the riverine trophic network and carrying capacity for fish     

Christiane Hudon  Antonella Cattaneo  Anne-Marie Tourville Poirier  Philippe Brodeur  Pierre Dumont  Yves Mailhot  Jean-Pierre Amyot  Simon-Pierre Despatie  Yves de Lafontaine 《Aquatic Sciences - Research Across Boundaries》2012,74(3):495-511

Submerged aquatic vegetation (SAV) constitutes a major component of fish habitat, providing support for epiphytes and invertebrates as well as shelter from predators. The effects of wetland epuration from a mesotrophic to a nearly oligotrophic state were examined over a 15?km long reach of the St. Lawrence River under the direct influence of major farmland tributaries. We hypothesized that the nutrient-enriched zone would support a higher biomass of SAV, epiphytes, macroinvertebrates and fish than the nitrogen-deficient epurated zone located downstream of the wetland. Predictions included that the enriched habitat would support a richer fish assemblage, with higher biomass and growth of juvenile yellow perch than found in the epurated zone. Results supported these hypotheses, demonstrating the chain of effects of nutrient reduction on the biomass of SAV (fourfold drop), invertebrate prey (ninefold), small (threefold) and large (1.5-fold) fish between the two zones. In addition to the reduction in SAV biomass, the replacement of filamentous chlorophytes by benthic mats of filamentous cyanobacteria in the epurated zone resulted in a less complex 3-D habitat structure and a low invertebrate availability for fish. Oligotrophication by wetland epuration exerted negative effects on fish habitat quality, food quantity and availability, with an impairment of juvenile perch growth and recruitment. A generalized model of the changes in habitat carrying capacity occurring with epuration (oligotrophication) or eutrophication is presented, with examples of other aquatic systems in which strong linkages between trophic status, SAV, invertebrates and fish productivity were also demonstrated.  相似文献   

Modeling propensity to move after job change using event history analysis and temporal GIS     

Marie-Hélène Vandersmissen  Anne-Marie Séguin  Marius Thériault  Christophe Claramunt 《Journal of Geographical Systems》2009,11(1):37-65

The research presented in this paper analyzes the emergent residential behaviors of individual actors in a context of profound social changes in the work sphere. It incorporates a long-term view in the analysis of the relationships between social changes in the work sphere and these behaviors. The general hypothesis is that social changes produce complex changes in the long-term dynamics of residential location behavior. More precisely, the objective of this paper is to estimate the propensity for professional workers to move house after a change of workplace. Our analysis draws on data from a biographical survey using a retrospective questionnaire that enables a posteriori reconstitution of the familial, professional and residential lifelines of professional workers since their departure from their parents’ home. The survey was conducted in 1996 in the Quebec City Metropolitan Area, which, much like other Canadian cities, has experienced a substantial increase in “unstable” work, even for professionals. The approach is based on event history analysis, a Temporal Geographic Information System and exploratory spatial analysis of model’s residuals. Results indicate that 48.9% of respondents moved after a job change and that the most important factors influencing the propensity to move house after a job change are home tenure (for lone adults as for couple) and number of children (for couples only). We also found that moving is associated with changing neighborhood for owners while tenants or co-tenants tend to stay in the same neighborhood. The probability of moving 1 year after a job change is 0.10 for lone adults and couples while after 2 years, the household structure seems to have an impact: the probability increased to 0.23 for lone adults and to 0.21 for couples. The outcome of this research contributes to furthering our understanding of a familial decision (to move) following a professional event (change of job), controlling for household structure, familial, professional and spatial contexts.

Marius ThériaultEmail:

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Stellar velocity profiles and line strengths out to four effective radii in the early-type galaxies NGC 3379 and 821     

Anne-Marie Weijmans  Michele Cappellari  Roland Bacon  P. T. de Zeeuw  Eric Emsellem  Jesús Falcón-Barroso  Harald Kuntschner  Richard M. McDermid  Remco C. E. van den Bosch  Glenn van de Ven † 《Monthly notices of the Royal Astronomical Society》2009,398(2):561-574

We use the integral-field spectrograph SAURON to measure the stellar line-of-sight velocity distribution and absorption line strengths out to four effective radii ( R _e) in the early-type galaxies NGC 3379 and 821. With our newly developed observing technique, we can now probe these faint regions in galaxies that were previously not accessible with traditional long-slit spectroscopy. We make optimal use of the large field-of-view and high throughput of the spectrograph: by adding the signal of all ∼1400 lenslets into one spectrum, we obtain sufficient signal-to-noise in a few hours of observing time to reliably measure the absorption line kinematics and line strengths out to large radius.
We find that the line strength gradients previously observed within 1 R _e remain constant out to at least 4 R _e, which puts constraints on the merger histories of these galaxies. The stellar halo populations are old and metal poor. By constructing orbit-based Schwarzschild dynamical models, we find that dark matter is necessary to explain the observed kinematics in NGC 3379 and 821, with 30–50 per cent of the total matter being dark within 4 R _e. The radial anisotropy in our best-fitting halo models is less than in our models without halo, due to differences in orbital structure. The halo also has an effect on the  Mg  b – V _esc  relation: its slope is steeper when a dark matter halo is added to the model.  相似文献   

Plant migration and plant communities at the time of the “green Sahara”     

Julie Watrin  Anne-Marie Lézine  Christelle Hély 《Comptes Rendus Geoscience》2009,341(8-9):656-670

Around 8500 cal years BP, at the time of the maximum of the African Humid Period, lakes and wetlands expanded in the present-day Sahara while large paleodrainages were formed or re-actived, in response to an orbitally-induced increase in monsoon rainfall. It has been suggested that the direct consequence of this increase in rainfall was the northward displacement of the Sahara/Sahel boundary, thought to have reached 23°N in central and eastern Africa. Here, we show a more complex situation characterized by an increase in biodiversity as the desert accommodated more humid-adapted species from tropical forests and wooded grasslands: tropical plant species now found some 400 to 500 km to the south probably entered the desert as gallery-forest formations along rivers and lakes where they benefited from permanent fresh water. At the same time, Saharan trees and shrubs persisted, giving rise to a vegetation that has no analogue today. In this article, we present distribution maps of selected plant species to show both the amplitude of the vegetation change compared to the present and the composition of the past plant communities. We also estimate the migration rate of tropical plant taxa to their northernmost position in the Sahara. This study is based on the use of several data sets: a data set of the modern plant distribution in northern Africa and a data set of modern and fossil pollen sites (from the African Pollen Database, http://fpd.mediasfrance.org/ and http://medias.obs-mip.fr/apd/).  相似文献   

A Compilation of Silicon and Thirty One Trace Elements Measured in the Natural River Water Reference Material SLRS-4 (NRC-CNRC)   总被引：1，自引：0，他引：1  

Delphine Yeghicheyan  Jean Carignan  Michel Valladon  Martine Bouhnik Le  Coz  Florence Le Cornec  Maryse Castrec-Rouelle  Michel Robert  Luc Aquilina  Emmanuel Aubry  Carine Churlaud  Aline Dia  Samuel Deberdt  Bernard Dupré  Rémi Freydier  Gérard Gruau  Odile Hénin  Anne-Marie de  Kersabiec  Joël Macé  Luc Marin  Nicole Morin  Patrice Petitjean  Elodie Serrat 《Geostandards and Geoanalytical Research》2001,25(2-3):465-474

The natural river water certified reference material SLRS-4 (NRC-CNRC, National Research Council-Conseil National de Recherches Canada) has been routinely analysed for major and trace elements by six French laboratories. Most measurements were made using inductively coupled plasma-mass spectrometry. For silicon and thirty one trace elements (rare earth elements, Ag, B, Br, Cs, Ga, Ge, Li, P, Pd, Rb, Se, Th, Ti, Tl, W, Y and Zr), no certified values are assigned by NRC-CNRC. We propose some compilation values and related uncertainties according to the results obtained by the different laboratories.  相似文献   

Late quaternary vegetation and climate of the Sahel     

Anne-Marie Lzine 《Quaternary Research》1989,32(3)

Pollen and phytogeographic evidence provides a vegetational history of the Sahel for the period 0–18,000 yr B.P. The zonal vegetation fluctuated latitudinally and its most extreme positions occurred at 18,000 and 8500 yr B.P. The first involved a southward shift of the Sahelian wooded grassland to 10°N under the arid conditions of the last glacial maximum. The second change shows a rapid northward migration of humid vegetation: Guinean elements reach 16°N and Sahelo-Sudanian elements extend to the southern margin of the modern Sahara (21°N) when the Atlantic monsoon flux increased. In the middle Holocene the extensive spread of Sudanian elements into the modern Sahelian zone suggests the appearance of a markedly dry season. The modern Sahelian semiarid conditions appeared abruptly at 2000 yr B.P.  相似文献