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We propose a new approach to model the geochemical evolution of continuously replenished and tapped steady-state magma chambers. We use a sinusoidal function to model cyclic magma supply. The temporal evolution of a reservoir is described using differential equations, in which the amount of refilling magma does not depend on the size of the chamber. These equations can be used to calculate incompatible trace element concentrations and magma quantities. We examine the geochemical consequences of episodic injections, noises and wall-rock assimilation. We also explore possible variations in crystallization rate. To show its potential, the theoretical treatment has been applied to the EPR 17-19°S, a site with a strong magma budget which has been the subject of several geological/geophysical studies. The practical application requires geological parameters to be constrained, as well as the extreme values of the lava concentration range. A first step specifies the incompatible trace element composition of the replenishing melt, which corresponds in the EPR case to a magnesian liquid (MgO = 9.5 wt%). It is then possible to determine other parameters such as cycle period (∼750 years), magma residence time (∼300 years), and reservoir size (from 4.1 to 8.6 km3 per 20 km segment). Lastly, variations in crystallization rate do not significantly alter the results. 相似文献
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Carole Cordier Martial Caroff Thierry Juteau Corinne Fleutelot Christophe Hmond Marion Drouin Joseph Cotten Claire Bollinger 《Lithos》2007,99(3-4):289-311
The present study is based on a set of lavas and crosscutting dikes collected by dives along detailed vertical transects on the northern flank of the western part of the Blanco Transform Fault, Northeast Pacific. The studied area consists of a small basin, the Western Blanco Depression (WBD), extending from the southern end of the Juan de Fuca ridge to a pseudofault trace 60 km eastward. The Northern Scarp of the WBD comprises a volcanic unit overlying a sheeted-dike complex. Major and trace element data, coupled with Sr–Nd isotope ratios, reveal a two-component mantle source, composed by an isotopically depleted matrix variably veined by more enriched material. One chemical group (NS2), indistinguishable from the other Northern Scarp samples on the basis of trace element data, has an unusually depleted isotopic composition typical of a nearly pure mantle end-member. Some cogenetic samples of the Northern Scarp have been used to constrain the differentiation modalities. Anorthite and MgO content profiles in plagioclase xenocrysts and phenocrysts reveal (i) the existence of H2O-bearing evolved melts in the mushy zones and (ii) the occurrence of mixing process between these melts and anhydrous mafic liquids. The hydration is supported by other petrographic features such as high magmatic fO2 values, calculated from Fe–Ti oxide pairs, and the presence of pyroxene inclusions in plagioclase phenocrysts. Mixing, consistent with the existence of Ni-rich ferrobasalts, is interpreted to be the consequence of the reservoir refilling by mafic liquids (Mg# = 70). These petrological and geochemical evidences are combined with the evolution of Mg# with depth to suggest a periodic open-system magma chamber evolution beneath the southern end of the Juan de Fuca ridge. 相似文献
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NJANKO Théophile FOZING Eric Martial KWéKAM Maurice YAKEU SANDJO Angéline Flore NJONFANG Emmanuel 《《地质学报》英文版》2012,86(1):73-84
The Fomopea granitic pluton is emplaced in gnessic and amphibolitic basement.These gneissic and amphibolitic basement rocks are represented in the pluton's body as sub-rounded,elongated or stretched xe... 相似文献
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Martial Haeffelin Jean-Charles Dupont Neda Boyouk Darrel Baumgardner Laurent Gomes Greg Roberts Thierry Elias 《Pure and Applied Geophysics》2013,170(12):2283-2303
Fog is an atmospheric phenomenon that has important environmental consequences related to visibility, air quality and climate change on local and regional scales. The formation of radiation fog results from a complex balance between surface radiative cooling, turbulent mixing in the surface layer, aerosol growth by deliquescence and activation of fog droplets. During the ParisFog field experiment, out of 16 events forecasted for radiation fog, activated fog materialized in seven events, while in five other events the visibility dropped to 1–2 km but haze particle size remained below the critical size of activation. To better understand the conditions that lead to or do not lead to sustained fog droplet activation, we performed a comparative study of dynamic, thermal, radiative and microphysical processes occurring between sunset and fog (or quasi-fog) onset. We selected two radiation fog events and two quasi-radiation fog events that occurred under similar large-scale conditions for this comparative study. We identified that aerosol growth by deliquescence and droplet activation actually occurred in both quasi-fog events, but only during <1 h. Based on ParisFog measurements, we found that the main factors limiting sustained activation of droplets at fog onset in the Paris metropolitan area are (1) lack of mixing in the surface layer (typically wind speed <0.5 ms?1), (2) relative humidity exceeding 90 % throughout the residual layer, (3) low cooling rate in the surface layer (typically less than ?1 °C per hour on average) due to weak radiative cooling (0 to ?30 Wm?2) and near zero sensible heat fluxes, and (4) a combination of the three factors listed above during the critical phase of droplet activation preventing the transfer of cooling from the surface to the liquid layer. In addition, we found some evidence of contrasted aerosol growth by deliquescence under high relative humidity conditions in the four events, possibly associated with the chemical nature of the aerosols, which could be another factor impacting droplet activation. 相似文献
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Valentin Bellassen Raphaël J. Manlay Jean-Pierre Chéry Vincent Gitz Assize Touré Martial Bernoux Jean-Luc Chotte 《Climatic change》2010,98(1-2):213-243
On the eve of the 15th climate negotiations conference in Copenhagen, the pressure to assess all climate mitigation options is mounting. In this study, a bio-physic model and a socio-economic model were designed and coupled to assess the carbon sequestration potential of agricultural intensification in Senegal. The biophysical model is a multiple linear regression, calibrated and tested on a dataset of long-term agricultural trials established in West Africa. The socio-economic model integrates both financial and environmental costs related to considered practice changes. Both models are spatially explicit and the resulting spatial patterns were computed and displayed over Senegal with a geographic information system. The national potential from large-scale intensification was assessed at 0.65–0.83 MtC. With regards to local-scaled intensification as local projects, the most profitable areas were identified in agricultural expansion regions (especially Casamance), while the areas that meet the current financial additionality criteria of the Clean Development Mechanism were located in the northern part of the Peanut Basin. Using the current relevant mode of carbon valuation (Certified Emission Reductions), environmental benefits are small compared to financial benefits. This picture is radically changed if “avoided deforestation”, a likely consequence of agricultural intensification, is accounted for as the greenhouse gases sink capacity of projects increases by an average of a hundred-fold over Senegal. 相似文献
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James B. Pollack Edwin F. Erickson Fred C. Witteborn Charles Chackerian Audrey L. Summers Warren Van Camp Betty J. Baldwin Gordon C. Augason Lawrence J. Caroff 《Icarus》1974,23(1):8-26
We have obtained measurements of Venus' reflection spectrum in the 1.2 to 4.1-μm spectral region from a NASA-Ames operated Lear jet. This was accomplished by observing both Venus and the sun with a spectrometer that contained a circular, variable interference filter, whose effective spectral resolution was 2%. The aircraft results were compared with computer generated spectra of a number of cloud candidates. The only substance which gave an acceptable match to the profile of Venus' strong 3-μm absorption feature, was a water solution of sulfuric acid, that had a concentration of 75% or more H2SO4 by weight. However, our spectra also show a modest decline in reflectivity from 2.3 μm towards 1.2-μm wavekength, which is inconsistent with the flat spectrum of sulfuric acid in this spectral region. We hypothesize that this decline is due to impurities in the sulfuric acid droplets.We also compared our list of cloud candidates with several other observed properties of the Venus clouds. While this comparison does not provide as unique an answer as did our analysis of the 3-μm band, we find that, in agreement with the results of Young (1973) and Sill (1973), concentrated sulfuric acid solutions are compatible with these additional observed properties of the Venus clouds. We conclude that the visible cloud layer of Venus is composed of sulfuric acid solution droplets, whose concentration is 75% H2SO4, or greater, by weight. 相似文献
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Jean-Philippe Clment Martial Caroff Patrick Dudoignon Patrick Launeau Marcel Bohn Joseph Cotten Sylvain Blais Grard Guille 《Lithos》2007,96(3-4):524-542
This paper reports new field observations and new petrological, textural and geochemical data on two gabbroic intrusions and one pegmatoid dyke from the French Polynesian islands Maupiti and Bora Bora, respectively. Olivine crystals from the Faataufi and Barque de Hiro gabbros (Maupiti) include High Temperature Iddingsite (HTI), exhibiting three distinct morphological facies. Chemical and crystallographical data performed by electron microprobe, scanning microscope, X-ray diffractometry and Near InfraRed spectroscopy show that HTI results from modifications of olivine structure through intense hydroxylation and Fe-oxidation. The HTI-free 120 m-wide Cloche de Hiro dyke (Bora Bora) exhibits a textural zonation from heterogranular/intergranular gabbro (peripheral part) to typical pegmatoid (inner area). We propose a textural tetrahedral classificatory diagram which can be used to clearly distinguish the textural characteristics of the pegmatoids from those of the other coarse-grained samples. Through comparison with a lava flow containing vesicle-rich segregation sheets, we suggest that the Cloche de Hiro dyke may correspond to a huge segregation structure derived from a Maupiti-type HTI-bearing gabbro through a vapor-differentiation process. Both intrusions might be considered as representative of two superposed levels in a vertically arranged magmatic complex. In this view, the Maupiti gabbroic bodies would represent the lower part of the postulated system. Under high oxygen fugacity, olivine crystals would have undergone important modifications of their structure, leading to HTI. The huge Bora Bora pegmatoid dyke would be the upper part of the complex. After expulsion from the HTI-bearing gabbroic solidification zone by build-up of gas pressure, vesicle-rich residual melt would have gathered into a shallow level and crystallized there as a pegmatoid body. 相似文献
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Jean-Philippe Clment Christelle Legendre Martial Caroff Herv Guillou Joseph Cotten Claire Bollinger Grard Guille 《Journal of Volcanology and Geothermal Research》2003,120(1-2):87-101
Occurrences of debris avalanche deposits newly identified in Tahiti (Society Islands) and Ua Huka (Marquesas Archipelago) are described and interpreted here. In both islands, the breccias are located within horseshoe-shaped residual calderas. In Tahiti, the epiclastic formations, up to 500 m thick, lie on the floor of the central depression and in the valley of the northwards running Papenoo River. In Ua Huka, the breccias crop out within a depression limited by a semicircular crest in four bays along the southern coast. Their thickness is ca. 100 m. A few clasts collected in the Tahitian breccias and some rocks forming their substratum have been dated (K–Ar datings) and analysed (major and trace elements, Sr–Nd isotopes) for this study. Using these data, we show that the debris avalanche(s) occurred in Tahiti Nui at the end of the growth of the shield volcano (between 570 000 and 390 000 years ago), maybe in consequence of the emplacement of the plutonic body which occupies the central part of the caldera. In Ua Huka, the collapse took place nearly 3 Ma ago, between the construction of the shield volcano and that of the inner one. The southwards orientation of the caldera, like that of the neighbouring island Nuku Hiva, might reflect a preferential direction of weakness in the substratum of the central Marquesas. 相似文献
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The spectrum of Saturn was measured from 80 to 350 cm?1 (29 to 125 μm) with ≈6-cm?1 resolution using a Michelson interferometer aboard NASA's Kuiper Airborne Observatory. These observations are of the full disk, with little contribution from the rings. For frequencies below 300 cm?1, Saturn's brightness temperature rises slowly, reaching ≈111°K at 100 cm?1. The effective temperature is 96.8 ± 2.5°K, implying that Saturn emits 3.0 ± 0.5 times as much energy as it receives from the Sun. The rotation-inversion manifolds of NH3 that are prominent in the far-infrared spectrum of Jupiter are not observed on Saturn. Our models predict the strengths to be only ≈2 to 5°K in brightness temperature because most of the NH3 is frozen out; this is comparable to the noise in our data. By combining our data with those of an earlier investigation when the Saturnicentric latitude of the Sun was B′ = 21.2°, we obtain the spectrum of the rings. The high-frequency end of the ring spectrum (ν > 230 cm?1) has nearly constant brightness temperature of 85°K. At lower frequencies, the brightness temperature decreases roughly as predicted by a simple absorption model with an optical depth proportional to ν1.5. This behavior could be due to mu-structure on the surface of the ring particles with a scale size of 10 to 100 μm and/or to impurities in their composition. 相似文献