L'érosion chimique et l'érosion mécanique à long terme du substrat granitique (Vendée,France)     

Jean-Christophe Maurin  Françoise Gilbert  Michel Robert  Carine Churlaud 《Comptes Rendus Geoscience》2005,337(9):841-848

We calculate the chemical depletion fraction of the granitic bedrock by analysing the rock-soil enrichment of zirconium. In Vendée (France), chemical weathering rates account for 26% of the denudation rates. Such a chemical depletion fraction characterizes temperate regimes. It is three times lower than that of humid tropical regimes. To cite this article: J.-C. Maurin et al., C. R. Geoscience 337 (2005).  相似文献   

Subglacial and ice-contact volcanism at the Öræfajökull stratovolcano, Iceland     

John A. Stevenson  David W. McGarvie  John L. Smellie  Jennie S. Gilbert 《Bulletin of Volcanology》2006,68(7-8):737-752

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Remote and in situ plume measurements of acid gas release from La Soufrière volcano, Guadeloupe     

Marie-Lise Bernard  Jack Molini  Rose-Helen Petit  Franois Beauducel  Gilbert Hammouya  Guy Marion 《Journal of Volcanology and Geothermal Research》2006,150(4):395-409

This paper presents the first remote measurements of La Soufrière gas emissions since the fumarolic and seismic reactivation in 1992. The chemical composition of the plumes has been measured from May 2003 to September 2004 using an Open Path Fourier Transform InfraRed (OP-FTIR) spectrometer, up to 15 m downwind the South Crater. HCl is clearly detected (concentration between 2.4 and 12 ppmv) whereas SO₂ and H₂S generally remain below the detection limit of the OP-FTIR. Direct measurements of SO₂ and H₂S near the South Crater with a Lancom III analyzer show a fast decrease of their concentrations with the distance. Calculated Cl / S mass ratios are high: from 9.4 ± 1.7 at 15 m from the vent to 2.8 ± 0.6 at 140 m. The enrichment in HCl of the gas emitted at La Soufrière, observed since 1998, corresponds to the degassing of a magma enriched in Cl and depleted in S. This result agrees with isotopic measurements which suggest a magmatic origin of the gases. Readjustments inside the volcanic system may have taken place during the seismic activity beginning in 1992 and enhance the transfer of magmatic gases to the summit.  相似文献   

The effect of open-marsh water management on summer bird populations on Topsail Island, North Carolina     

Gilbert S. Grant  William W. Kirby-Smith 《Estuaries and Coasts》1998,21(2):361-363

Open-marsh water management (OMWM) manipulates selected areas of an estuarine marsh by constructing narrow, deep ditches that harbor resident populations of predators of mosquito larvae. It does not, however, alter the surrounding vegetation by deposition of spoil mounds. We censused the summer (breeding and nonbreeding) bird populations in two adjacent salt marsh sites on Topsail Island, North Carolina, for two summers before OMWM ditching occurred and for four seasons postditching. A total of 53 nonbreeding species and five breeding species of birds were encountered on the study sites. None of the interannual changes in bird populations can be attributed to OMWM.  相似文献   

Geochronology and geochemistry of multiple generations of monazite from the Wepawaug Schist,Connecticut, USA: implications for monazite stability in metamorphic rocks   总被引：1，自引：0，他引：1  

A. Lanzirotti  Gilbert N. Hanson 《Contributions to Mineralogy and Petrology》1996,125(4):332-340

 U-Pb isotope analyses, rare earth and trace element analyses, and petrographic observations are presented for monazites from the Wepawaug Schist in southern Connecticut, USA. Two samples of kyanite zone schist were collected less than a meter apart. Each sample contains a different variety of monazite with distinct morphology, chemistry, and Pb isotopic composition. One sample preserves a largely amphibolite facies mineralogy, including kyanite, staurolite, garnet, biotite, and chlorite, with little textural evidence of later shearing. Monazites from this sample are xenoblastic with about 1 wt% ThO₂, 0.3 wt% CaO, and a more LREE enriched pattern than monazites from the second sample. These xenoblastic monazites preserve textural evidence of a retrograde reaction to apatite which involves chlorite, indicating that these monazites became unstable during retrograde chloritization of biotite. These monazites give strongly discordant U-Pb ages which fit a chord with an upper intercept age of 411±18 Ma, interpreted as the minimum growth age of these xenoblastic monazites, perhaps during amphibolite facies metamorphism. The second sample contains S-C banding, evidence of dynamic recrystallization, and abundant retrograde chlorite. This sample contains idioblastic monazites with about 3 wt% ThO₂, 0.8 wt% CaO, and with less fractionated REE patterns. These monazites give close to concordant U-Pb ages with a mean ²⁰⁷Pb*/²⁰⁶Pb* age of 388 ± 2 Ma. This age is interpreted as probably representing the time of monazite growth during retrogression of the sample from an amphibolite to greenschist facies mineralogy. Received: 26 June 1995/Accepted: 25 May 1996  相似文献   

Sequential Inductively Coupled Plasma Determination Of Some Rare-Earth Elements in Five French Geostandards   总被引：1，自引：0，他引：1  

Iwan ROELANDTS  Gilbert MICHEL 《Geostandards and Geoanalytical Research》1986,10(2):135-154

Experimental data for eleven rare-earth elements (REE) obtained by inductively coupled plasma spectrometry (ICP) in five French geochemical reference standards (BE-N, BR, DR-N, GS-N and FK-N)are presented. The method is based on acid digestion of the sample and cation-exchange separation from matrix elements.
Together with these new determinations an updated compilation of these reference materials are presented. Good agreement between the present results and previously preferred and published values obtained by various analytical techniques is observed. The values obtained in the present work corroborate the validity of the outlined method.  相似文献   

Effect of a dolerite intrusion on triterpane stereochemistry and kerogen in Rundle oil shale,Australia     

Trevor D. Gilbert  Lorraine C. Stephenson  R.Paul Philp 《Organic Geochemistry》1985,8(2):163-169

Stereochemical changes of triterpanes present in extracts from an immature oil shale sequence intruded by a 3-m dolerite sill have been studied by gas chromatography-mass spectrometry (GC-MS). The steric configuration of the hopanes was observed to change from one dominated by the thermally less stable 17β(H), 21β(H) configuration at some distance from the intrusion, to one dominated by the thermally more stable 17α(H), 21β(H) and 17β(H), 21α(H) configurating in the immediate vicinity of the intrusion. In addition, severe alteration of the kerogen appeared to have taken place as a result of the contact metamorphism, and high concentrations of extractable organic matter were observed below the intrusion. Characterization of the kerogens by Curie-point pyrolysis has enabled the effects of the intrusion on the shales to be monitored.  相似文献   

DISCUSSION OF "The Practical Application of Surface Electrical Resistivity to Detection of Ground-Water Pollution," by Daniel W. Urish     

Patricia J. Leonard-Mayer  Gilbert Gabanski 《Ground water》1984,22(3):342-343

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Breaking global temperature records after Mt. Pinatubo     

Gilbert W. Bassett Jr.  Zhiyong Lin 《Climatic change》1993,25(2):179-184

The probability of setting global temperature records is reconsidered in light of cooling due to the Mt. Pinatubo eruption. The cooling resets temperature by moving it away from the top of its 100-year range. Depending on the statistical model for temperature, this reset can lead to a much lower probability for a record in the next few years. The exercise illustrates how record setting depends on the underlying model, the current record value, and - if there is serial correlation- the current temperature.  相似文献   

The Guiana and the West African Shield Palaeoproterozoic grouping: new palaeomagnetic data for French Guiana and the Ivory Coast     

Sébastien Nomade  Yan Chen  ré Pouclet  Gilbert Féraud  Hervé Théveniaut  Bertin Yao Daouda  Max Vidal  Cécile Rigolet 《Geophysical Journal International》2003,154(3):677-694

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