Melting relations of a magnesian abyssal tholeiite and the origin of MORBs     

Toshitsugu Fujii  Henri Bougault 《Earth and Planetary Science Letters》1983,62(2):283-295

Melting relations of a glassy magnesian olivine tholeiite from the FAMOUS area have been studied within the pressure range 1 atm to 15 kbar. From 1 atm to 10 kbar, olivine is the liquidus phase, followed by plagioclase and Ca-rich clinopyroxene. Above 10 kbar, Ca-rich clinopyroxene appears on the liquidus, followed by orthopyroxene and spinel. Near 10 kbar, olivine, orthopyroxene, clinopyroxene, spinel and plagioclase crystallize within 10°C of the liquidus. This indicates that a liquid of this magnesian olivine tholeiite composition could coexist with mantle peridotite at about 10 kbar. This result is in agreement with the geochemistry of Ni; the Ni concentration of the studied sample corresponds to the theoretical concentration in a primary magma [14,15].These data suggest that at least some magnesian mid-oceanic ridge basalts (MORBs) could be primary melts segregated from the mantle at depths near the transition zone between plagioclase lherzolite and spinel lherzolite (about 10 kbar). Based on this model, the residual mantle after extraction of MORBs should be lherzolite, not harzburgite.High-pressure (7–10 kbar) fractionation models involving olivine, plagioclase and clinopyroxene, which have been proposed by several workers (e.g. [36]) to explain the varieties of MORBs, were re-emphasized based on this melting study. The rare occurrence of clinopyroxene as a phenocryst phase in MORBs is explained by precipitation in a magma chamber at high pressure, or by dissolution of clinopyroxene formed earlier at high pressure.  相似文献   

Dissolved organic carbon in pore waters from a hypersaline environment     

W. M. Berry Lyons  Henri E. Gaudette  Heidi C. Gustafson 《Organic Geochemistry》1981,3(4):133-135

Pore waters were collected from a sea-marginal, hypersaline pond in the Sinai and analyzed for dissolved organic carbon (DOC). The pore water DOC values ranged from 121 to 818 mg 1⁻¹ with maxima between 15 and 54 cm deep. These values are some of the highest observed from recent sediments and probably reflect production via abiotic as well as biotic sources.  相似文献   

On the combined adjustment of a gravimetrically determined geoid and GPS levelling stations     

Zhiheng Jiang  Henri Duquenne 《Journal of Geodesy》1996,70(8):505-514

Summary A new basic geodetic network using the GPS technique is now being set up in France. There will be altogether 1000 benchmarks connected to the French levelling network. Obviously, the GPS levelling points are not dense enough to produce a national levelling reference surface. A gravimetrically determined geoid has therefore been proposed to be used for the interpolation between the GPS levelling points. However, because of long-wavelength errors, we consider that a gravimetric geoid does not have sufficient accuracy. A regression by fitting the gravimetrically determined geoid to the GPS levelling points is generally proposed. Unfortunately, this country-wide geoid fitting work cannot eliminate local deformations in the geoid, which happen in areas where there are errors or shortages of gravity or DTM data. This paper proposes and discusses a combined adjustment method. The principle is to divide up the geoid into small pieces and then to adjust them to the GPS levelling points locally with constraint conditions for the common points of the adjacent pieces. In order to benefit from the advantages of the high resolution and high relative accuracy of the gravimetric geoid, as well as the high absolute accuracy of the GPS levelling points, we establish respectively a relative observation equation for the difference of the gravimetric geoid undulation and an absolute observation equation for the GPS levelling points. Finally, we adjust the observation equations as a whole. Several global and local systematic errors are also taken into account and some special cases, such as adjustment in groups and blunder detection, are also discussed.  相似文献   

Capelin (Mallotus villosus) as an important food source for northern fulmars (Fulmarus glacialis) breeding at Bjornoya (Bear Island), Barents Sea     

Cherel  Yves; Ridoux  Vincent; Weimerskirch  Henri; Tveraa  Torkild; Chastel  Olivier 《ICES Journal of Marine Science》2001,58(1):355-361

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The cambridge cosmochemistry symposium     

Henri E. Mitler 《Icarus》1973,20(1):54-71

This article is a critical summary of the solar-system aspects of a meeting held in August 1972. The purpose of the meeting was to review work done sonce the 1967 Paris meeting on the Origin of the Elements.The principal topics discussed were element abundances; the structure and composition of comets, of the terrestrial and the outer planets, of the Moon, of exospheric dust, and of meteorites; planetary atmospheres; evidence for a protosolar magnetic field from remanent meteorite magnetism, abiotic synthesis of organic molecules; nucleosynthesis; solar cosmic rays; and meteorite ages.The principal results were these: There have been a number of significant changes in the estimated solar abundances—especially D, He, B, and Fe. A great deal of progress has been made in our understanding of the temperature and pressure conditions in the protosolar nebula during planetary formation, and of the condensation of solids in it. It is believed that the bulk chemistry of the terrestrial planets is now understood on the basis of equilibrium (slow) cooling of the nebula. Their atmospheres are consistent with this model, and that of Jupiter, with inhomogeneous accretion. The structure of Jupiter is also better understood. There is disagreement on the deep structure and composition of the Moon, though of course an enormous amount has been learned, especially about the surface layers. Not so much progress has been made in understanding comets.  相似文献   

Grain size dependency in the occurrence of sand waves     

Hennie Henriët van der Veen  Suzanne Jacqueline Marie Hélène Hulscher  Michiel Adrianus Frederik Knaapen 《Ocean Dynamics》2006,56(3-4):228-234

Sandy shallow seas, like the North Sea, are very dynamic. Several morphological features are present on the bed, from small ripples to sand waves and large tidal sandbanks. The larger patterns induce significant depth variations that have an impact on human activities taking place in this area. Therefore, it is important to know where these large-scale features occur, what their natural behaviour is and how they interact with human activities. Here, we extend earlier research that compares the results of an idealized model of large-scale seabed patterns with data of seabed patterns in the North Sea. The idealized model is extended with a grain size dependency. The adaptations lead to more accurate predictions of the occurrence of large-scale bed forms in the North Sea. Therefore, grain size dependency and, in particular, critical shear stress are important to explain the occurrence of sand waves and sandbanks in the North Sea. Responsible Editor: Alejandro Souza  相似文献   

Comparative Rates of Western Juniper Afforestation in South‐Central Oregon and the Role of Anthropogenic Disturbance*     

Peter T. Soul  Paul A. Knapp  Henri D. Grissino‐Mayer 《The Professional geographer》2003,55(1):43-55

We examine changes in canopy cover for adult western juniper from the 1960s to 1994 in central Oregon using repeat aerial photography. We compare changes at four sites with a land‐use history of minimal anthropogenic disturbance to changes on adjacent sites that have a disturbance history more typical of central Oregon rangelands. Canopy cover increased at all sites, but afforestation on sites with domestic livestock grazing was greater. The potential driving forces common to all sites include a long fire‐free interval, early twentieth‐century favorable climatic conditions, biological inertia, and atmospheric CO₂ enrichment.  相似文献   

The terminal bulk Lorentz factor of relativistic electron–positron jets     

N. Renaud  & G. Henri 《Monthly notices of the Royal Astronomical Society》1998,300(4):1047-1056

We present a numerical simulation of the bulk Lorentz factor of a relativistic electron–positron jet driven by the Compton rocket effect from accretion disc radiation. The plasma is assumed to have a power-law distribution n _e(γ) ∝ γ^{− s} with 1 < γ < γ_max and is continuously reheated to compensate for radiation losses. We include the full Klein–Nishina (hereafter KN) cross-section, and study the role of the energy upper cut-off γ_max, spectral index s and source compactness. We determine the terminal bulk Lorentz factor in the cases of supermassive black holes, relevant to AGN, and stellar black holes, relevant to galactic microquasars. In the latter case, Klein–Nishina cross-section effects are more important and induce a terminal bulk Lorentz factor smaller than in the former case. Our result are in good agreement with bulk Lorentz factors observed in Galactic (GRS 1915+105, GRO J1655−40) and extragalactic sources. Differences in scattered radiation and acceleration mechanism efficiency in the AGN environment can be responsible for the variety of relativistic motion in those objects. We also take into account the influence of the size of the accretion disc; if the external radius is small enough, the bulk Lorentz factor can be as high as 60.  相似文献   

40Ar-39Ar ages of biotites from Corsica and arguments for Permian age of alkaline granitic intrusion     

Henri Maluski 《Contributions to Mineralogy and Petrology》1976,58(3):305-317

The Western part of Corsica is underlain by Variscan calcalkaline granites which intrude the pre-Variscan basement. These granites and their basement are also intruded by Permian hyperalkaline granites. Overprinted biotites of the basement and the calcalkaline granites show only one plateau age at about 250 m.y., except for a sample of calcalkaline granite from the Cargèse region which has a high temperature plateau age of 330 m.y. related to the emplacement and a low temperature plateau age of 230 m.y. Plateau ages around 250 m.y. due to the intrusion of hyperalkaline granites whose biotites give plateau ages between 250 and 280 m.y. reflect this important thermal event.  相似文献   

Groundwater fluctuations and footslope ferricrete soils in the humid tropical zone of southern Cameroon     

Emile Temgoua  Henri‐Bosko Djeuda Tchapnga  Emile Tanawa  Claire Guenat  Hans‐Rudolf Pfeifer 《水文研究》2005,19(16):3097-3111

This paper discusses the relationship between the differentiation of ferruginous accumulations and the variable water saturation of footslope soil patterns. An analysis of the slope morphology of a typical hill in the forest zone of southern Cameroon and a seasonal survey of the levels of groundwaters, springs and rivers were considered in relation to the petrology of different soil patterns. The study site is a tabular hillock whose slopes present a progressive development from steep to gentle slopes. The variable residence time of water within the soil, creating an alternation of reducing and oxidizing conditions, affects soil chemistry, structure and lateral extension of the soil patterns. The ferruginous soil patterns, being formed on the footslopes, gradually increase in extent with decreasing slope angle and the relative rise of the groundwater level. The steep footslopes, where groundwater has a shorter residence time, show a soft mottled clay pattern, restricted to the bottom part of the slope. The moderate footslopes exhibit a deep permanent and a temporary perched groundwater table. The latter, with its regular capillary fringe, contributes to more reducing conditions within isolated domains in the soil patterns, and thus to the alternation with oxidizing conditions, generating a continuous hard soil pattern (massive carapace). The more gently dipping footslopes exhibit groundwater levels near the surface and also a significant amplitude of groundwater fluctuation. Iron, previously accumulated in moderate footslope patterns, is reduced, remobilized, and leached. The soil patterns formed develop into a variegated carapace, more extended along the slope, containing less iron, but nevertheless more hardened, due to the important fluctuations of the groundwater table. These patterns are limited to the zone of groundwater fluctuation and deteriorate as the water fluctuation zone recedes. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献